publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
|---|---|---|---|
2020-09-30 | Domain Control by Adjusting Anisotropic Stress in Pyrochlore Oxide Cd2Re2O7 | The 5d pyrochlore oxide Cd2Re2O7 exhibits successive phase transitions from a
cubic pyrochlore structure (phase I) to a tetragonal structure without
inversion symmetry below Ts1 of ~200 K (phase II) and further to another
noncentrosymmetric tetragonal structure below Ts2 of ~120 K (phase III). The
two low-temperature phases may be characterized by odd-parity multipolar orders
induced by the Fermi liquid instability of the spin-orbit-coupled metal. To
control the tetragonal domains generated by the transitions and to obtain a
single-domain crystal for the measurements of anisotropic properties, we
prepared single crystals with the (0 0 1) surface and applied biaxial and
uniaxial stresses along the plane. Polarizing optical microscopy observations
revealed that inducing a small strain of approximately 0.05% could flip the
twin domains ferroelastically in a reversible fashion at low temperatures,
which evidences that the tetragonal deformation switches at Ts2 between c > a
for phase II and c < a for phase III. Resistivity measurements using
single-domain crystals under uniaxial stress showed that the anisotropy was
maximum at around Ts2 and turned over across Ts2: resistivity along the c axis
is larger (smaller) than that along the a axis by ~25% for phase II (III) at
around Ts2. These large anisotropies probably originate from spin-dependent
scattering in the spin-split Fermi surfaces of the cluster electric toroidal
quadrupolar phases of Cd2Re2O7. | 2009.14443v1 |
2012-01-10 | Microscopic theory for a ferromagnetic-nanowire/superconductor heterostructure: Transport, fluctuations and topological superconductivity | Motivated by the recent experiment of Wang et al. [Nature Physics 6, 389
(2010)], who observed a highly unusual transport behavior of ferromagnetic
Cobalt nanowires proximity-coupled to superconducting electrodes, we study
proximity effect and temperature-dependent transport in such a mesoscopic
hybrid structure. It is assumed that the asymmetry in the tunneling barrier
gives rise to the Rashba spin-orbit-coupling in the barrier that enables
induced p-wave superconductivity in the ferromagnet to exist. We first develop
a microscopic theory of Andreev scattering at the spin-orbit-coupled interface,
derive a set of self-consistent boundary conditions, and find an expression for
the p-wave minigap in terms of the microscopic parameters of the contact.
Second, we study temperature-dependence of the resistance near the
superconducting transition and find that it should generally feature a
fluctuation-induced peak. The upturn in resistance is related to the
suppression of the single-particle density of states due to the formation of
fluctuating pairs, whose tunneling is suppressed. In conclusion, we discuss
this and related setups involving ferromagnetic nanowires in the context of
one-dimensional topological superconductors. It is argued that to realize
unpaired end Majorana modes, one does not necessarily need a half-metallic
state, but a partial spin polarization may suffice. Finally, we propose yet
another related class of material systems -- ferromagnetic semiconductor wires
coupled to ferromagnetic superconductors -- where direct realization of
Kitaev-Majorana model should be especially straightforward. | 1201.2180v2 |
2016-03-14 | Lifshitz scaling effects on holographic paramagnetism/ferromagneism phase transition | In the probe limit, we investigate holographic paramagnetism-ferromagnetism
phase transition in the four-dimensional (4D) and five-dimensional(5D) Lifshitz
black holes by means of numerical and semi-analytical methods, which is
realized by introducing a massive 2-form field coupled to the Maxwell field. We
find that the Lifshitz dynamical exponent $z$ contributes evidently to magnetic
moment and hysteresis loop of single magnetic domain quantitatively not
qualitatively. Concretely, in the case without external magnetic field, the
spontaneous magnetization and ferromagnetic phase transition happen when the
temperature gets low enough, and the critical exponent for the magnetic moment
is always $1/2$, which is in agreement with the result from mean field theory.
And the increasing $z$ enhances the phase transition and increases the DC
resistivity which behaves as the colossal magnetic resistance effect in some
materials. Furthermore, in the presence of the external magnetic field, the
magnetic susceptibility satisfies the Cure-Weiss law with a general $z$. But
the increase of $z$ will result in shortening the period of the external
magnetic field. | 1603.04149v1 |
2016-03-14 | Double-phase transition and giant positive magnetoresistance in the quasi-skutterudite Gd$_3$Ir$_4$Sn$_{13}$ | The magnetic, thermodynamic and electrical/thermal transport properties of
the caged-structure quasi-skutterudite Gd$_3$Ir$_4$Sn$_{13}$ are
re-investigated. The magnetization $M(T)$, specific heat $C_p(T)$ and the
resistivity $\rho(T)$ reveal a double-phase transition -- at $T_{N1}\sim$ 10~K
and at $T_{N2}\sim$ 8.8~K -- which was not observed in the previous report on
this compound. The antiferromagnetic transition is also visible in the thermal
transport data, thereby suggesting a close connection between the electronic
and lattice degrees of freedom in this Sn-based quasi-skutterudite. The
temperature dependence of $\rho(T)$ is analyzed in terms of a power-law for
resistivity pertinent to Fermi liquid picture. Giant, positive
magnetoresistance (MR) $\approx$ 80$\%$ is observed in Gd$_3$Ir$_4$Sn$_{13}$ at
2~K with the application of 9~T. The giant MR and the double magnetic
transition can be attributed to the quasi-cages and layered antiferromagnetic
structure of Gd$_3$Ir$_4$Sn$_{13}$ vulnerable to structural distortions and/or
dipolar or spin-reorientation effects. The giant value of MR observed in this
class of 3:4:13 type alloys, especially in a Gd-compound, is the highlight of
this work. | 1603.04377v1 |
2016-03-29 | Electronic and transport properties of the Mn-doped topological insulator Bi$_{2}$Te$_{3}$: A first-principles study | We present a first-principles study of the electronic, magnetic, and
transport properties of the topological insulator Bi$_{2}$Te$_{3}$ doped with
Mn atoms in substitutional (Mn$_{\rm Bi}$) and interstitial van der Waals gap
positions (Mn$_{\rm i}$), which act as acceptors and donors, respectively. The
effect of native Bi$_{\rm Te}$- and Te$_{\rm Bi}$-antisite defects and their
influence on calculated electronic transport properties is also investigated.
We have studied four models representing typical cases, namely (i)
Bi$_{2}$Te$_{3}$ with and without native defects, (ii) Mn$_{\rm Bi}$ defects
with and without native defects, (iii) the same but for Mn$_{\rm i}$ defects,
and (iv) the combined presence of Mn$_{\rm Bi}$ and Mn$_{\rm i}$. It was found
that lattice relaxations around Mn$_{\rm Bi}$ defects play an important role
for both magnetic and transport properties. The resistivity is strongly
influenced by the amount of carriers, their type, and by the relative positions
of the Mn-impurity energy levels and the Fermi energy. Our results indicate
strategies to tune bulk resistivities, and also help to uncover the location of
Mn atoms in measured samples. Calculations indicate that at least two of the
considered defects have to be present simultaneously in order to explain the
experimental observations, and the role of interstitials may be more important
than expected. | 1603.08811v2 |
2017-04-03 | Thickness-dependent Kapitza resistance in multilayered graphene and other two-dimensional crystals | The Kapitza or thermal boundary resistance (TBR), which limits heat
dissipation from a thin film to its substrate, is a major factor in the thermal
management of ultrathin nanoelectronic devices and is widely assumed to be a
property of only the interface. However, data from experiments and molecular
dynamics simulations suggest that the TBR between a multilayer 2-dimensional
(2D) crystal and its substrate decreases with increasing film thickness. To
explain this thickness dependence, we generalize the recent theory for
single-layer 2D crystals by Ong, Cai and Zhang [Phys. Rev. B 94, 165427
(2016)], which is derived from the theory by Persson, Volokitin, and Ueba [J.
Phys.: Condens. Matter 23, 045009 (2011)], and use it to evaluate the TBR
between bare $N$-layer graphene and SiO$_{2}$. Our calculations reproduce
quantitatively the TBR thickness dependence seen in experiments and simulations
as well as its asymptotic convergence, and predict that the low-temperature TBR
scales as $T^{-4}$ in few-layer graphene. Analysis of the interfacial
transmission coefficient spectrum shows that the TBR reduction in few-layer
graphene is due to the additional contribution from higher flexural phonon
branches. Our theory sheds light on the role of flexural phonons in
substrate-directed heat dissipation and provides the framework for optimizing
the thermal management of multilayered 2D devices. | 1704.00435v2 |
2017-04-23 | Quantum limit transport and destruction of the Weyl nodes in TaAs | Weyl fermions are a new ingredient for correlated states of electronic
matter. A key difficulty has been that real materials also contain non-Weyl
quasiparticles, and disentangling the experimental signatures has proven
challenging. We use magnetic fields up to 95 tesla to drive the Weyl semimetal
TaAs far into its quantum limit (QL), where only the purely chiral 0th Landau
levels (LLs) of the Weyl fermions are occupied. We find the electrical
resistivity to be nearly independent of magnetic field up to 50 tesla: unusual
for conventional metals but consistent with the chiral anomaly for Weyl
fermions. Above 50 tesla we observe a two-order-of-magnitude increase in
resistivity, indicating that a gap opens in the chiral LLs. Above 80 tesla we
observe strong ultrasonic attenuation below 2 kelvin, suggesting a
mesoscopically-textured state of matter. These results point the way to
inducing new correlated states of matter in the QL of Weyl semimetals. | 1704.06944v3 |
2017-05-01 | Arbitrary control of the polarization and intensity profiles of diffraction-attenuation-resistant beams along their propagation direction | We report on the theory and experimental generation of a class of
diffraction-attenuation-resistant beams with state of polarization (SoP) and
intensity that can be controlled on demand along the propagation direction.
This is achieved by a suitable superposition of Bessel beams, whose parameters
are systematically chosen based on closed-form analytic expressions provided by
the Frozen Waves (FWs) method. Using an amplitude-only spatial light modulator,
we experimentally demonstrate three scenarios. In the first, the SoP of a
horizontally polarized beam evolves to radial polarization and is then changed
to vertical polarization, with the beam intensity held constant. In the second,
we simultaneously control the SoP and the longitudinal intensity profile, which
was chosen such that the beam's central ring can be switched-off over
predefined space regions, thus generating multiple foci with different SoP and
at different intensity levels along the propagation. Finally, the ability to
control the SoP while overcoming attenuation inside lossy fluids is shown
experimentally for the first time in the literature (to the best of our
knowledge). Therefore, we envision our proposed method to be of great interest
for many applications, such as optical tweezers, atom guiding, material
processing, microscopy, and optical communications. | 1705.00408v3 |
2019-03-02 | Topological Valley Currents in Bilayer Graphene/Hexagonal Boron Nitride Superlattices | Graphene superlattices have recently been attracting growing interest as an
emergent class of quantum metamaterials. In this paper, we report the
observation of nonlocal transport in bilayer graphene (BLG) superlattices
encapsulated between two hexagonal boron nitride (hBN) layers, which formed
hBN/BLG/hBN moir\'e superlattices. We then employed these superlattices to
detect a long-range charge-neutral valley current using an all-electrical
method. The moir\'e superlattice with broken inversion symmetry leads to a hot
spot with Berry curvature accumulating at the charge neutral point (CNP), and
it harbors satellites of the CNP. We observed nonlocal resistance on the order
of 1 $\text{k}\Omega$, which obeys a scaling relation. This nonlocal resistance
evolves from the quantum Hall effect but without magnetic field/time-reversal
symmetry breaking, which is associated with a hot-spot-induced topological
valley current. This study should pave the way to developing a
Berry-phase-sensitive probe to detect hot spots in gapped Dirac materials with
inversion-symmetry breaking. | 1903.00625v2 |
2019-04-05 | Explicit relationship between electrical and topological degradation of polymer-supported metal films subjected to mechanical loading | For a comprehensive characterization of mechanical reliability of
metallization layers on polymer substrates both electrical and mechanical
degradation should be taken into account. Although it is evident that cracking
of a conductive film should lead to electrical degradation, the quantitative
relationship between the growth of electric resistance and parameters of the
induced crack pattern has remained thus far unexplored. With the help of finite
element modelling we were able to find an explicit and concise expression which
shows that electrical resistance grows with the fourth order of the crack
length and second order of the areal crack density. The discovered relationship
was verified by comparison with the experimental results of tensile testing of
polymer-supported thin metal films. Presented model is independent of the
length scale and can be applied to films with different thicknesses as long as
Ohm's law is valid. It is demonstrated that linear crack density is an
ambiguous parameter which does not properly capture the development of a crack
pattern. For the unambiguous characterization of the intensity of a crack
pattern a universal dimensionless factor is proposed. Presented results show
that there is a wide range of possible crack patterns which do not lead to
electrical failure of a conductive film that can be used for failure-free
design of flexible electronic devices. | 1904.03007v1 |
2015-04-09 | Quantum oscillations with non-zero Berry phase from a complex three dimensional Fermi surface in Bi2Te3 | We performed angle dependent magnetoresistance study of a metallic single
crystal sample of Bi2Te3. We find that the magnetoresistance is highly
asymmetric in positive and negative magnetic fields for small angles between
the magnetic field and the direction perpendicular to the plane of the sample.
The magnetoresistance becomes symmetric as the angle approaches 90 degree. The
quantum Shubnikov de-Haas oscillations are symmetric and show signatures of
topological surface states with Dirac dispersion in the form of non-zero Berry
phase. However, the angular dependence of these oscillations suggests a complex
three dimensional Fermi surface as the source of these oscillations, which does
not exactly conform with the six ellipsoidal model of the Fermi surface of
Bi2Te3. We attribute the asymmetry in the magnetoresistance to a mixing of the
Hall voltage in the longitudinal resistance due to the comparable magnitude of
the Hall and longitudinal resistance in our samples. This provides a clue to
understanding the asymmetric magnetoresistance often seen in this and similar
materials. Moreover, the asymmetric nature evolves with exposure to atmosphere
and thermal cycling, which we believe is either due to exposure to atmosphere
or thermal cycling, or both affecting the carrier concentration and hence the
Hall signal in these samples. However, the quantum oscillations seem to be
robust against these factors which suggests that the two have different
origins. | 1504.02386v1 |
2015-06-17 | Origin of the glass-like dynamics in molecular metals $\pmbκ$-(BEDT-TTF)$_{\textbf{2}}$X: implications from fluctuation spectroscopy and $\pmb{\textit{ab initio}}$ calculations | We have studied the low-frequency dynamics of the charge carriers in
different organic charge-transfer salts $\kappa$-(BEDT-TTF)$_2$X with polymeric
anions X by using resistance noise spectroscopy. Our aim is to investigate the
structural, glass-like transition caused by the conformational degrees of
freedom of the BEDT-TTF molecules' terminal ethylene groups. Although of
fundamental importance for studies of the electronic ground-state properties,
the phenomenology of the glassy dynamics is only scarcely investigated and its
origin is not understood. Our systematic studies of fluctuation spectroscopy of
various different compounds reveal a universal, pronounced maximum in the
resistance noise power spectral density related to the glass transition. The
energy scale of this precess can be identified with the activation energy of
the glass-like ethylene endgroup structural dynamics as determined from
thermodynamic and NMR measurements. For the first time for this class of
'plastic crystals', we report a typical glassy property of the relaxation time,
namely a Vogel-Fulcher-Tammann law, and are able to determine the degree of
fragility of the glassy system. Supporting $\textit{ab initio}$ calculations
provide an explanation for the origin and phenomenology of the glassy dynamics
in different systems in terms of a simple two-level model, where the relevant
energy scales are determined by the coupling of the ethylene endgroups to the
anions. | 1506.05191v1 |
2015-07-13 | Structural, and Magnetic properties of flux free large FeTe Single crystal | We report synthesis of non superconducting parent compound of iron
chalcogenide, i.e., FeTe single crystal by self flux method. The FeTe single
crystal is crystallized in tetragonal structure with the P4/nmm space group.
The detailed SEM (scanning electron microscopy) results showed that the
crystals are formed in slab like morphology and are near (slight deficiency of
Te) stoichiometric with homogenous distribution of Fe and Te. The coupled
structural and magnetic phase transition is seen at around 70K in both
electrical resistivity and magnetization measurements, which is hysteric
(deltaT = 5K) in nature with cooling and warming cycles. Magnetic
susceptibility (chi-T) measurements showed the magnetic transition to be of
antiferromagnetic nature, which is substantiated by isothermal magnetization
(M-H) plots as well. The temperature dependent electrical resistivity measured
in 10kOe field in both in plane and out of plane field directions showed that
the hysteric width nearly becomes double to deltaT = 10K, and is maximum for
the out of plane field direction for the studied FeTe single crystal. We also
obtained a sharp spike like peak in heat capacity Cp(T) measurement due to the
coupled structural and magnetic order phase transitions. | 1507.03320v2 |
2018-12-06 | Covalent-bonding-induced strong phonon scattering in the atomically thin WSe2 layer | In nano-device applications using 2D van der Waals materials, a heat
dissipation through nano-scale interfaces can be a critical issue for
optimizing device performances. By using a time-domain thermoreflectance
measurement technique, we examine a cross-plane thermal transport through
mono-layered (n=1) and bi-layered (n=2) WSe2 flakes which are sandwiched by top
metal layers of Al, Au, and Ti and the bottom Al2O3 substrate. In these
nanoscale structures with hetero- and homo-junctions, we observe that the
thermal boundary resistance (TBR) is significantly enhanced as the number of
WSe2 layers increases. In particular, as the metal is changed from Al, to Au,
and to Ti, we find an interesting trend of TBR depending on the WSe2 thickness;
when referenced to TBR for a system without WSe2, TBR for n=1 decreases, but
that for n=2 increases. This result clearly demonstrates that the stronger
bonding for Ti leads to a better thermal conduction between the metal and the
WSe2 layer, but in return gives rise to a large mismatch in the phonon density
of states between the first and second WSe2 layers so that the WSe2-WSe2
interface becomes a major thermal resistance for n=2. By using photoemission
spectroscopy and optical second harmonic generation technique, we confirm that
the metallization induces a change in the valence state of W-ions, and also
recovers a non-centrosymmetry for the bi-layered WSe2. | 1812.02383v1 |
2018-12-25 | Quantum Transport in Topological Semimetals under Magnetic Fields (II) | We review our recent works on the quantum transport, mainly in topological
semimetals and also in topological insulators, organized according to the
strength of the magnetic field. At weak magnetic fields, we explain the
negative magnetoresistance in topological semimetals and topological insulators
by using the semiclassical equations of motion with the nontrivial Berry
curvature. We show that the negative magnetoresistance can exist without the
chiral anomaly. At strong magnetic fields, we establish theories for the
quantum oscillations in topological Weyl, Dirac, and nodal-line semimetals. We
propose a new mechanism of 3D quantum Hall effect, via the "wormhole" tunneling
through the Weyl orbit formed by the Fermi arcs and Weyl nodes in topological
semimetals. In the quantum limit at extremely strong magnetic fields, we find
that an unexpected Hall resistance reversal can be understood in terms of the
Weyl fermion annihilation. Additionally, in parallel magnetic fields,
longitudinal resistance dips in the quantum limit can serve as signatures for
topological insulators. | 1812.10120v2 |
2019-06-11 | Observation of Large Unidirectional Rashba Magnetoresistance in Ge(111) | Relating magnetotransport properties to specific spin textures at surfaces or
interfaces is an intense field of research nowadays. Here, we investigate the
variation of the electrical resistance of Ge(111) grown epitaxially on
semi-insulating Si(111) under the application of an external magnetic field. We
find a magnetoresistance term which is linear in current density j and magnetic
field B, hence odd in j and B, corresponding to a unidirectional
magnetoresistance. At 15 K, for I = 10 $\mu$A (or j = 0.33 A/m) and B = 1 T, it
represents 0.5 % of the zero field resistance, a much higher value compared to
previous reports on unidirectional magnetoresistance. We ascribe the origin of
this magnetoresistance to the interplay between the externally applied magnetic
field and the current-induced pseudo-magnetic field in the spin-splitted
subsurface states of Ge(111). This unidirectional magnetoresistance is
independent of the current direction with respect to the Ge crystal axes. It
progressively vanishes, either using a negative gate voltage due to carrier
activation into the bulk (without spin-splitted bands), or by increasing the
temperature due to the Rashba energy splitting of the subsurface states lower
than $\sim$58 k$_B$. The highly developed technologies on semiconductor
platforms would allow the rapid optimization of devices based on this
phenomenon. | 1906.04457v1 |
2019-06-11 | Thermal conductivity and thermal rectification of nanoporous graphene: A molecular dynamics simulation | Using non-equilibrium molecular dynamics (NEMD) simulation, we study thermal
properties of the so-called nanoporous graphene (NPG) sheet which contains a
series of nanoporous in an ordered way and was synthesized recently (Science
360 (2018), 199). The dependence of thermal conductivity on sample size, edge
chirality, and porosity concentration are investigated. Our results indicate
that the thermal conductivity of NPG is about two orders smaller compared with
of pristine graphene. Therefore this sheet can be used as a thermoelectric
material. Also, the porosity concentration helps us to tune the thermal
conductivity. Moreover, the results show that the thermal conductivity
increases with growing sample length due to ballistic transport. On the other
hand, along the armchair direction, the thermal conductivity is larger than
zigzag direction. We also examined the thermal properties of the interface of
NPG and graphene. The temperature drops significantly through the interface
leading to the thermal resistance. The thermal resistance changes with imposed
heat flux direction, and this difference cause significantly large thermal
rectification factor, and heat current prefers one direction to another.
Besides, to investigate those quantities fundamentally, we study the phonon
density of states and scattering of them. | 1906.04696v1 |
2019-06-12 | Spin transport and Spin Tunnelling Magneto-Resistance (STMR) of F$|$NCSC$|$F spin valve | In this work, we study the spin transport at the
Ferromagnet$|$Noncentrosymmetric Superconductor (F$|$NCSC) junction of a
Ferromagnet$|$Noncentrosymmetric Superconductor$|$Ferromagnet (F$|$NCSC$|$F)
spin valve. We investigate the Tunnelling Spin-Conductance (TSC), spin current
and Spin Tunnelling Magneto-Resistance (STMR), and their dependence on various
important parameters like Rashba Spin-Orbit Coupling (RSOC), strength and
orientation of magnetization, an external in-plane magnetic field, barrier
strength and a significant Fermi Wavevector Mismatch (FWM) at the ferromagnetic
and superconducting regions. The study has been carried out for different
singlet-triplet mixing of the NCSC gap parameter. We develop Bogoliubov-de
Gennes (BdG) Hamiltonian and use the extended Blonder - Tinkham - Klapwijk
(BTK) approach along with the scattering matrix formalism to calculate the
scattering coefficients. Our results strongly suggest that the TSC is highly
dependent on RSOC, magnetization strength and its orientation, and
singlet-triplet mixing of the gap parameter. It is observed that NCSC with
moderate RSOC shows maximum conductance for a partially opaque barrier in
presence of low external magnetic field. For a strongly opaque barrier and a
nearly transparent barrier a moderate value and a low value of field
respectively are found to be suitable. Moreover, NCSC with large singlet
component is appeared to be useful. In addition, for NCSC with large RSOC and
low magnetization strength, a giant STMR ($\%$) is observed. We have also seen
that the spin current is strongly magnetization orientation dependent. With the
increase in bias voltage spin current increases in transverse direction, but
the component along the direction of flow is almost independent. | 1906.05081v1 |
2019-06-13 | Passivation-induced physicochemical alterations of the native surface oxide film on 316L austenitic stainless steel | Time of Flight Secondary Ion Mass Spectroscopy, X-Ray Photoelectron
Spectroscopy, in situ Photo-Current Spectroscopy and electrochemical analysis
were combined to characterize the physicochemical alterations induced by
electrochemical passivation of the surface oxide film providing corrosion
resistance to 316L stainless steel. The as-prepared surface is covered by a ~2
nm thick, mixed (Cr(III)-Fe(III)) and bi-layered hydroxylated oxide. The inner
layer is highly enriched in Cr(III) and the outer layer less so. Molybdenum is
concentrated, mostly as Mo(VI), in the outer layer. Nickel is only present at
trace level. These inner and outer layers have band gap values of 3.0 and
2.6-2.7 eV, respectively, and the oxide film would behave as an insulator.
Electrochemical passivation in sulfuric acid solution causes the preferential
dissolution of Fe(III) resulting in the thickness decrease of the outer layer
and its increased enrichment in Cr(III) and Mo(IV-VI). The further Cr(III)
enrichment of the inner layer causes loss of photoactivity and improved
corrosion protection with the anodic shift of the corrosion potential and the
increase of the polarization resistance by a factor of ~4. Aging in the passive
state promotes the Cr enrichment in the inner barrier layer of the passive
film. | 1906.05544v1 |
2019-06-21 | Crystal Growth and basic transport and magnetic properties of MnBi2Te4 | We report successful growth of magnetic topological insulator (MTI) MnBi2Te4.
The heating schedule basically deals with growth of the crystal from melt at
900C and very slow cooling (1C/hr) to around 600C with 24 hours hold time,
followed by cooling to room temperature. Our detailed, PXRD Reitveld analysis
showed that the resultant crystal is dominated mainly by MnBi2Te4 and minor
phases of Bi2Te3 and MnTe. The transport measurements showed a step like
behavior at around 150K followed by cusp like structure in resistivity at
around 25K (TP) due reported anti-ferromagnetic ordering of Mn. Both the
resistivity transitions are seen clearly in dR/dT measurements at 150K and 20K
respectively. The 25K transition of the compound is also seen in magnetic
susceptibility. Low temperature (5K) magnetoresistance (MR) in applied field of
up to 6 Tesla exhibited negative ve MR below 3 Tesla and +ve for higher fields.
Also, seen are steps in MR below one Tesla. The studied MnBi2Te4 MTI crystal
could be a possible candidate for Quantum Anomalous Hall (QAH) effect. | 1906.09038v3 |
2019-10-03 | Nonlinear transport of ballistic Dirac electrons tunneling through a tunable potential barrier in graphene | Dirac-electronic tunneling and nonlinear transport properties with both
finite and zero energy bandgap are investigated for graphene with a tilted
potential barrier under a bias. For validation, results from a
finite-difference based numerical approach, which is developed for calculating
transmission and reflection coefficients with a dynamically-tunable
(time-dependent bias field) barrier-potential profile, are compared with those
of both an analytical model for a static square-potential barrier and a
perturbation theory using Wentzel-Kramers-Brillouin (WKB) approximation. For a
biased barrier, both transmission coefficient and tunneling resistance are
computed and analyzed, indicating a full control of the peak in tunneling
resistance by bias field for a tilted barrier, gate voltage for barrier height,
and energy for incoming electrons. Moreover, a finite energy gap in graphene is
found to suppress head-on transmission as well as skew transmission with a
large transverse momentum. For a gapless graphene, on the other hand, filtering
of Dirac electrons outside of normal incidence is found and can be used for
designing electronic lenses. All these predicted attractive transport
properties are expected extremely useful for the development of novel
electronic and optical graphene-based devices. | 1910.01295v1 |
2019-10-09 | Decoupling of itinerant and localized $d$-orbital electrons in the compound Sc$_{0.5}$Zr$_{0.5}$Co | By using the arc-melting method, we successfully synthesized the compound
Sc$_{0.5}$Zr$_{0.5}$Co with the space group of $Pm$-$3m$. Both the resistivity
and magnetic susceptibility measurements reveal a phase transition at about 86
K. This transition might be attributed to the establishment of an
antiferromagnetic order. The magnetization hysteresis loop measurements in wide
temperature region show a weak ferromagnetic feature, which suggests a possible
canted arrangement of the magnetic moments. Bounded by the phase transition
temperature, the resistivity at ambient pressure shows a change from Fermi
liquid behavior to a super-linear behavior as temperature increases. By
applying pressures up to 32.1 GPa, the transition temperature does not show a
clear change and no superconductivity is observed above 2 K. The density
functional theory (DFT) calculations confirm the existence of the
antiferromagnetic order and reveal a gap between the spin-up and spin-down
$d$-orbital electrons. This kind of behavior may suggest that the
antiferromagnetic order in this compound originates from the localized
$d$-electrons which do not contribute to the conductance. Thus the itinerant
and localized $d$-orbital electrons in the compound are decoupled. | 1910.03966v1 |
2019-10-10 | AFM manipulation of gold nanowires to build electrical circuits | We introduce scanning-probe-assisted nanowire circuitry (SPANC) as a new
method to fabricate electrodes for the characterization of electrical transport
properties at the nanoscale. SPANC uses an atomic force microscope (AFM) to
manipulate nanowires to create complex and highly conductive nanostructures
(paths) that work as nanoelectrodes, allowing connectivity and electrical
characterization of other nano-objects. The paths are formed by the spontaneous
cold welding of gold nanowires upon mechanical contact, leading to an excellent
contact resistance of about 9 Ohms/junction. SPANC is an easy to use and
cost-effective technique that fabricates clean nanodevices. Hence, this new
method can complement and/or be an alternative to other well-established
methods to fabricate nanocircuits such as electron beam lithography (EBL). The
circuits made by SPANC are easily reconfigurable, and their fabrication does
not require the use of polymers and chemicals. In this work, we present a few
examples that illustrate the capabilities of this method, allowing robust
device fabrication and electrical characterization of several nano-objects with
sizes down to aprox. 10 nm, well below the current smallest size able to be
contacted in a device using the standard available technology (around 30 nm).
Importantly, we also provide the first experimental determination of the sheet
resistance of thin antimonene flakes. | 1910.04801v1 |
2019-10-21 | A report of (topological) Hall anomaly two decades ago in Gd2PdSi3, and its relevance to the history of the field of Topological Hall Effect due to magnetic skyrmions | The area of magnetic skyrmions, with potential revolution in certain
applications, in condensed matter physics is considered about a decade old. In
this article, we draw the attention of the community to the recent work of
Kurumaji et al [Science 365, 914 (2019)] establishing magnetic skyrmion lattice
behavior in Gd2PdSi3. We consider it important to bring out the two decades old
history, in particular Hall transport anomalies characterizing magnetic
skyrmions. The key experimental data in support of the skyrmion lattice that
Kurumaji et al present is the observation of topological Hall resistivity in an
intervening field range, following two metamagnetic transitions. In addition,
the values are giant, compared to those known for other magnetic skyrmions. We
point out here that such features in Hall resistivity data, arising from Gd 4f
magnetism, can be found in our publication in 1999 (along with the metamagnetic
transitions) and we expressed difficulties in explaining the results at that
time. In view of above, we propose to the scientific community that the
compound Gd2PdSi3, ex post facto, can be considered as the first experimental
demonstration for giant topological Hall effect in this field, discovered about
two decades ago. We take this opportunity to share some thoughts, offering
clues for further investigations, in particular to identify novel magnetic
skyrmions and to find the same to enable applications. | 1910.09194v2 |
2019-10-25 | Energy-efficient ultrafast SOT-MRAMs based on low-resistivity spin Hall metal Au0.25Pt0.75 | Many key electronic technologies (e.g., large-scale computing, machine
learning, and superconducting electronics) require new memories that are fast,
reliable, energy-efficient, and of low-impedance at the same time, which has
remained a challenge. Non-volatile magnetoresistive random access memories
(MRAMs) driven by spin-orbit torques (SOTs) have promise to be faster and more
energy-efficient than conventional semiconductor and spin-transfer-torque
magnetic memories. This work reports that the spin Hall effect of
low-resistivity Au0.25Pt0.75 thin films enables ultrafast antidamping-torque
switching of SOT-MRAM devices for current pulse widths as short as 200 ps. If
combined with industrial-quality lithography and already-demonstrated
interfacial engineering, our results show that an optimized MRAM cell based on
Au0.25Pt0.75 can have energy-efficient, ultrafast, and reliable switching, e.g.
a write energy of < 1 fJ (< 50 fJ) for write error rate of 50% (<1e-5) for 1 ns
pulses. The antidamping torque switching of the Au0.25Pt0.75 devices is 10
times faster than expected from a rigid macrospin model, most likely because of
the fast micromagnetics due to the enhanced non-uniformity within the free
layer. These results demonstrate the feasibility of Au0.25Pt0.75-based
SOT-MRAMs as a candidate for ultrafast, reliable, energy-efficient,
low-impedance, and unlimited-endurance memory. | 1910.11896v2 |
2019-11-15 | Resist and Transfer Free Patterned CVD Graphene Growth on ALD Molybdenum Carbide Nano Layers | Multilayer graphene (MLG) films were grown by chemical vapour deposition
(CVD) on molybdenum carbide ($MoC_{x}$) substrates. We fabricated the catalytic
$MoC_{x}$ films by plasma enhanced atomic layer deposition (PEALD). The
mechanism of graphene growth is studied and analysed for amorphous and
crystalline $MoC_{x}$ films. In addition, the unique advantages of catalytic
substrate PEALD are demonstrated in two approaches to graphene device
fabrication. First, we present a complete bottom up, resist-free patterned
graphene growth (GG) on pre-patterned $MoC_{x}$ PEALD performed at
50$^{\circ}C$. Selective CVD GG eliminates the need to pattern or transfer the
graphene film to retain its pristine, as grown, qualities. Furthermore, we
fabricated MLG directly on PEALD $MoC_{x}$ on 100 nm suspended SiN membrane. We
characterise the MLG qualities using Raman spectroscopy, and analyse the
samples by optical microscopy, scanning electron microscopy and X-ray
diffraction measurements. The techniques of graphene device manufacturing
demonstrated here pave the path for large scale production of graphene
applications. | 1911.06490v3 |
2020-05-30 | Tribocorrosion under galvanic interaction of Ti6Al4V and NiCr implant alloys | Micromovements that occur in the joint between dental prostheses and implants
can lead to wear-induced degradation. This process can be enhanced by corrosion
in the oral environment influenced by the presence of solutions containing
fluoride. Moreover, the eventual galvanic interactions between NiCr and Ti
alloys can accelerate the wear-corrosion process. In this work, the
tribocorrosion process of Ti6Al4V and NiCr alloys used in dental implant
rehabilitations immersed in fluoride solutions at different pH values was
investigated. The galvanic interaction effect between the alloys was also
assessed. Tribocorrosion tests in corrosive media were performed with isolated
Ti6Al4V and NiCr alloys, followed by testing with both alloys in contact. The
media selected were based on fluoride concentrations and pH values that are
possible to be found in oral environments. Analysis of the surfaces after the
tribocorrosion tests was carried out using confocal laser microscopy. The wear
profile and volume losses were determined by confocal measurements. It was
concluded that the galvanic interaction between the alloys increased the
tribocorrosion resistance of Ti6Al4V, compared with that of the isolated
Ti6Al4V alloy. Ti6Al4V coupled with NiCr reduced the electrochemical potential
decay during sliding. The increased resistance was explained by the
electrochemical shift of the Ti6Al4V potential from active dissolution to the
passive domain. | 2006.00270v1 |
2020-10-16 | Multiscale studies of nanoconfined charging dynamics in supercapacitors bridged by machine learning | The energy-delivery performance of supercapacitors is fundamentally
determined by the dynamics of ions confined in nanoporous materials, which has
attracted intensive interest in nanoscopic research. Many nanoscopic
understandings, including changes in in-pore ion concentration and mobility
during dynamical processes, are continuously reported. However, quantitative
scale-up of these nanoscopic understandings for evaluation of the macroscopic
performance of supercapacitors is difficult due to the absence of links between
these scales. Here we demonstrate that machine learning can be used to
establish such links. Starting from nanoscale, we first reveal a
diffusion-enhanced migration of ions in nanopores using primarily modified
Poisson-Nernst-Planck model, unlike in bulk electrolyte where diffusion
counteracts migration. Using machine learning, we discover a dynamically
varying ionic resistance and its equation, resulting from the in-pore ion
concentration change contributed by diffusion-enhanced migration. The obtained
equation is used to construct a nano-circuitry model (NCM), which describes
both the macroscopic performance of supercapacitors and nanometre-resolved
ionic behaviour. We demonstrate that NCM can provide additional perspectives to
understand cyclic voltammograms. A Faradaic-like current peak can show in
non-Faradaic processes, and an asymmetric charging/discharging can occur
without ion desolvation. These is because the dynamically varying resistance
delivers ions effectively for storage. The demonstrated use of machine learning
could extend to other ionic systems including batteries and desalination,
paving the route towards rational design. | 2010.08151v1 |
2020-10-31 | A Non-Volatile Cryogenic Random-Access Memory Based on the Quantum Anomalous Hall Effect | The interplay between ferromagnetism and topological properties of electronic
band structures leads to a precise quantization of Hall resistance without any
external magnetic field. This so-called quantum anomalous Hall effect (QAHE) is
born out of topological correlations, and is oblivious of low-sample quality.
It was envisioned to lead towards dissipationless and topologically protected
electronics. However, no clear framework of how to design such an electronic
device out of it exists. Here we construct an ultra-low power, non-volatile,
cryogenic memory architecture leveraging the QAHE phenomenon. Our design
promises orders of magnitude lower cell area compared with the state-of-the-art
cryogenic memory technologies. We harness the fundamentally quantized Hall
resistance levels in moir\'e graphene heterostructures to store non-volatile
binary bits (1, 0). We perform the memory write operation through controlled
hysteretic switching between the quantized Hall states, using nano-ampere level
currents with opposite polarities. The non-destructive read operation is
performed by sensing the polarity of the transverse Hall voltage using a
separate pair of terminals. We custom design the memory architecture with a
novel sensing mechanism to avoid accidental data corruption, ensure highest
memory density and minimize array leakage power. Our design is transferrable to
any material platform exhibiting QAHE, and provides a pathway towards realizing
topologically protected memory devices. | 2011.00170v1 |
2021-02-11 | Microscopic metallic air-bridge arrays for connecting quantum devices | We present a single-exposure fabrication technique for a very large array of
microscopic air-bridges using a tri-layer resist process with electron-beam
lithography. The technique is capable of forming air-bridges with strong
metal-metal or metal-substrate connections. This was demonstrated by its
application in an electron tunnelling device consisting of 400 identical
surface gates for defining quantum wires, where the air-bridges are used as
suspended connections for the surface gates. This technique enables us to
create a large array of uniform one-dimensional channels that are open at both
ends. In this article, we outline the details of the fabrication process,
together with a study and the solution of the challenges present in the
development of the technique, which includes the use of water-IPA (isopropyl
alcohol) developer, calibration of resist thickness and numerical simulation of
the development. | 2102.06123v2 |
2021-03-29 | In Situ Phase-Transition Crystallization of All-Inorganic Water-Resistant Exciton-Radiative Heteroepitaxial CsPbBr3-CsPb2Br5 Core-Shell Perovskite Nanocrystals | The instability of metal halide perovskites upon exposure to moisture or heat
strongly hampers their applications in optoelectronic devices. Here, we report
the large-yield synthesis of highly water-resistant total-inorganic green
luminescent CsPbBr3/CsPb2Br5 core/shell heteronanocrystals (HNCs) by developing
an in situ phase transition approach. It is implemented via water-driven phase
transition of the original monoclinic CsPbBr3 nanocrystal and the resultant
tetragonal CsPb2Br5 nanoshell has small lattice mismatch with the CsPbBr3 core,
which ensures formation of an epitaxial interface for the yielded
CsPbBr3/CsPb2Br5 HNCs. These HNCs maintain nearly 100% of the original
luminescence intensity after immersion in water for eleven months and the
luminescence intensity drops only to 81.3% at 100 {\deg}C. The transient
luminescence spectroscopy and density functional theory calculation reveal that
there are double radiative recombination channels in the core CsPbBr3
nanocrystal, and the electron potential barrier provided by the CsPb2Br5
nanoshell significantly improves the exciton recombination rate. A prototype
quasi-white light-emitting device based on these robust CsPbBr3/CsPb2Br5 HNCs
is realized, showing their strong competence in solid-state lighting and wide
color-gamut displays. | 2103.15491v2 |
2021-05-31 | Ab initio Molecular Dynamics Simulation of Threshold Displacement Energies and Defect Formation Energies in Y4Zr3O12 | Ab initio molecular dynamics simulations using VASP was employed to calculate
threshold displacement energies and defect formation energies of Y4Zr3O12
{\delta}-phase, which is the most commonly found phase in newly developed Zr
and Al-containing ODS steels. The Threshold displacement energy (Ed) values are
determined to be 28 eV for Zr3a primary knock-on atom along [111] direction, 40
eV for Zr18f atoms along [111] direction and 50 eV for Y recoils along [110]
direction. Minimum Ed values for O and O' atoms are 13 eV and 16 eV
respectively. The displacement energies of anions are much smaller compared to
cations, thus suggesting that anion disorder is more probable than cation
disorder. All directions except the direction in which inherent structural
vacancies are aligned, cations tend to occupy another cation site. The
threshold displacement energies are larger than that of Y2Ti2O7, the
conventional precipitates in Ti containing ODS steels. Due to the partial
occupancy of Y and Zr in the 18f position, the antisite formation energy is
negligibly small, and it may help the structure to withstand more disorder upon
irradiation. These results convey that Zr/Al ODS alloys, which have better
corrosion resistance properties compared to the conventional Ti-ODS alloys, may
also possess superior radiation resistance. | 2105.15066v1 |
2021-06-10 | Multilayer Capacitances: How Selective Contacts Affect Capacitance Measurements of Perovskite Solar Cells | Capacitance measurements as a function of voltage, frequency and temperature
are useful tools to identify fundamental parameters that affect solar cell
operation. Techniques such as capacitance-voltage (CV), Mott-Schottky analysis
and thermal admittance spectroscopy (TAS) measurements are therefore frequently
employed to obtain relevant parameters of the perovskite absorber layer in
perovskite solar cells. However, state-of-the-art perovskite solar cells employ
thin electron and hole transport layers that improve contact selectivity. These
selective contacts are often quite resistive in nature, which implies that
their capacitances will contribute to the total capacitance and thereby affect
the extraction of the capacitance of the perovskite layer. Based on this
premise, we develop a simple multilayer model that considers the perovskite
solar cell as a series connection of the geometric capacitance of each layer in
parallel with their voltage-dependent resistances. Analysis of this model
yields fundamental limits to the resolution of spatial doping profiles and
minimum values of doping/trap densities, built-in voltages and activation
energies. We observe that most of the experimental
capacitance-voltage-frequency-temperature data, calculated doping/trap
densities and activation energies reported in literature are within these
cut-off values derived, indicating that the capacitance response of the
perovskite solar cell is indeed strongly affected by the capacitance of its
selective contacts. | 2106.05758v2 |
2021-06-25 | Blistering Failure of Elastic Coatings with Applications to Corrosion Resistance | A variety of polymeric surfaces, such as anti-corrosion coatings and
polymer-modified asphalts, are prone to blistering when exposed to moisture and
air. As water and oxygen diffuse through the material, dissolved species are
produced, which generate osmotic pressure that deforms and debonds the
coating.These mechanisms are experimentally well-supported; however,
comprehensive macroscopic models capable of predicting the formation osmotic
blisters, without extensive data-fitting, is scant. Here, we develop a general
mathematical theory of blistering and apply it to the failure of anti-corrosion
coatings on carbon steel. The model is able to predict the irreversible,
nonlinear blister growth dynamics, which eventually reaches a stable state,
ruptures, or undergoes runaway delamination, depending on the mechanical and
adhesion properties of the coating. For runaway delamination, the theory
predicts a critical delamination length, beyond which unstable corrosion-driven
growth occurs. The model is able to fit multiple sets of blister growth data
with no fitting parameters. Corrosion experiments are also performed to observe
undercoat rusting on carbon steel, which yielded trends comparable with model
predictions. The theory is used to define three dimensionless numbers which can
be used for engineering design of elastic coatings capable of resisting visible
deformation, rupture, and delamination. | 2106.13371v1 |
2021-07-29 | Thermal Contribution in the Electrical Switching Experiments with Heavy Metal / Antiferromagnet Structures | We examine the thermal origin of the detected "saw-tooth" shaped Hall
resistance (Rxy) signals in the spin-orbit torque switching experiment for
antiferromagnetic MnN. Compared with the results of the heavy metal /
antiferromagnet bilayers (MnN/Ta), the qualitatively same "saw-tooth" shaped
signals also appear in the samples with the heavy metal layer alone (either Ta
or Pt) without MnN layer. In addition, The Rxy signal changes oppositely in the
devices with Ta and Pt, due to the opposite temperature coefficient of
resistivity (TCR) of the two materials. All those results are consistent with
the "localized Joule heating" mechanism in devices with Hall crosses geometry.
Moreover, by utilizing a structure with separated writing current paths and
Hall cross area, the quadratic relationship between delta-Rxy and the writing
current's amplitude is observed, which provides quantitative evidence of the
thermal contribution. These results reveal the dominant thermal artifact in the
widely used Hall crosses geometry for Neel vector probing, and also provide a
strategy to semi-quantitatively evaluate the thermal effect, which can shed
light on a more conclusive experiment design. | 2107.13859v1 |
2021-08-26 | Direct thermal infrared vision via nanophotonic detector design | Detection of infrared (IR) photons in a room-temperature IR camera is carried
out by a two-dimensional array of microbolometer pixels which exhibit
temperature-sensitive resistivity. When IR light coming from the far-field is
focused onto this array, microbolometer pixels are heated up in proportion to
the temperatures of the far-field objects. The resulting resistivity change of
each pixel is measured via on-chip electronic readout circuit followed by
analog to digital (A/D) conversion, image processing, and presentation of the
final IR image on a separate information display screen. In this work, we
introduce a new nanophotonic detector as a minimalist alternative to
microbolometer such that the final IR image can be presented without using the
components required for A/D conversion, image processing and display. In our
design, the detector array is illuminated with visible laser light and the
reflected light itself carries the IR image which can be directly viewed. We
realize and numerically demonstrate this functionality using a resonant
waveguide grating structure made of typical materials such as silicon carbide,
silicon nitride, and silica for which lithography techniques are
well-developed. We clarify the requirements to tackle the issues of fabrication
nonuniformities and temperature drifts in the detector array. We envision a
potential near-eye display device for IR vision based on timely use of
diffractive optical waveguides in augmented reality headsets and tunable
visible laser sources. Our work indicates a way to achieve direct thermal IR
vision for suitable use cases with lower cost, smaller form factor, and reduced
power consumption compared to the existing thermal IR cameras. | 2108.11583v1 |
2021-08-26 | Effects of minor alloying on the mechanical properties of Al based metallic glasses | Minor alloying is widely used to control mechanical properties of metallic
glasses (MGs). The present understanding of how a small amount of alloying
element changes strength is that the additions lead to more efficient packing
of atoms and increased local topological order, which then increases the
barrier for shear transformations and the resistance to plastic deformation.
Here, we discover that minor alloying can improve the strength of MGs by
increasing the chemical bond strength alone and show that this strengthening is
distinct from changes in topological order. The results were obtained using
Al-Sm based MGs minor alloyed with transition metals (TMs). The addition of TMs
led to an increase in the hardness of the MGs which, however, could not be
explained based on changes in the topological ordering in the structure.
Instead we found that it was the strong bonding between TM and Al atoms which
led to a higher resistance to shear transformation that resulted in higher
strength and hardness, while the topology around the TM atoms had no influence
on their mechanical response. This finding demonstrates that the effects of
topology and chemistry on mechanical properties of MGs are independent of each
other and that they should be understood as separate, sometimes competing
mechanisms of strengthening. This understanding lays a foundation for design of
MGs with improved mechanical properties. | 2108.12028v1 |
2021-09-13 | Ray Optics for Gliders | Control of self-propelled particles is central to the development of many
microrobotic technologies, from dynamically reconfigurable materials to
advanced lab-on-a-chip systems. However, there are few physical principles by
which particle trajectories can be specified and can be used to generate a wide
range of behaviors. Within the field of ray optics, a single principle for
controlling the trajectory of light -- Snell's law -- yields an intuitive
framework for engineering a broad range of devices, from microscopes to cameras
and telescopes. Here we show that the motion of self-propelled particles
gliding across a resistance discontinuity is governed by a variant of Snell's
law, and develop a corresponding ray optics for gliders. Just as the ratio of
refractive indexes sets the path of a light ray, the ratio of resistance
coefficients is shown to determine the trajectories of gliders. The magnitude
of refraction depends on the glider's shape, in particular its aspect ratio,
which serves as an analog to the wavelength of light. This enables the demixing
of a polymorphic, many-shaped, beam of gliders into distinct monomorphic,
single-shaped, beams through a friction prism. In turn, beams of monomorphic
gliders can be focused by spherical and gradient friction lenses.
Alternatively, the critical angle for total internal reflection can be used to
create shape-selective glider traps. Overall our work suggests that furthering
the analogy between light and microscopic gliders will result in a wide range
of new devices for sorting, concentrating, and analyzing self-propelled
particles. | 2109.06360v5 |
2021-10-11 | Topological phonons in an inhomogeneously strained silicon-2: Evidence of spin-momentum locking | In this study, we report first experimental evidence of spin-momentum locking
in the topological phonons in an inhomogeneously strained Si thin film. The
spin-momentum locking in the topological phonons lead to a longitudinal spin
texture or spatially inhomogeneous spin distribution in the freestanding sample
structure. The spin texture was uncovered using location dependent Hall effect
and planar Hall effect measurement. The charge carrier density and anomalous
Hall resistance showed a linear behavior along the length of the sample.
Similarly, the planar Hall resistance related with the spin dependent
scattering was also found to be different at two different location along the
length of the sample. The spin-momentum locking also gave rise to transverse
thermal spin current and spin-Nernst magneto thermopower response, which was
uncovered using angle dependent longitudinal second harmonic measurement. The
magneto thermopower response was also a function of crystallography of the Si
sample where the sign of the response was opposite for <110> and <100> aligned
samples. The spin-momentum locking in topological phonons may give rise to
large spin dependent response at and above room temperature, which can pave the
way for energy efficient spintronics and spin-caloritronics devices. | 2110.04937v1 |
2021-10-11 | Bi kagome sublattice distortions by quenching and flux pinning in superconducting RbBi$_2$ | The properties of RbBi$_2$, a 4.15 K superconductor, were investigated using
magnetic field, pressure and neutron diffraction. Under hydrostatic pressure,
an almost 50 % reduction of T$_c$ is observed, linked to a low Debye
temperature estimated at 165 K. The resistivity and magnetic susceptibility
were measured on quenched and slow-cooled polycrystalline samples. The
resistivity follows a low temperature power-law dependence in both types of
samples, while the diamagnetic susceptibility, $\chi$, is dependent on the
sample cooling history. Slow-cooled samples have a $\chi= -1$ while quenched
samples have $\chi< -1$ due to grain size differences. Evidence of the effects
of the cooling rate is also discerned from the local structure, obtained by
neutron diffraction and the pair density function analysis. Slow-cooled samples
have structurally symmetric Bi hexagons, in contrast to quenched samples in
which disorder is manifested in periodic distortions of the Bi hexagonal rings
of the kagome sublattice. Disorder may lead to flux pinning that reduces vortex
mobility, but T$_c$ remains unaffected by the cooling rate. | 2110.05452v1 |
2021-10-18 | Magnetic field induced transition from a vortex liquid to Bose metal in ultrathin a-MoGe thin film | We identify a magnetic field induced transition from a vortex liquid to Bose
metal in a 2-dimensional amorphous superconductor, a-MoGe, using a combination
of magnetotransport and scanning tunnelling spectroscopy (STS). Below the
superconducting transition, Tc ~ 1.36 K, the magnetoresistance isotherms cross
at a nearly temperature independent magnetic field, H_c^*~ 36 kOe. Above this
field, the temperature coefficient of resistance is weakly negative, but the
resistance remains finite as T --> 0, as expected in a bad metal. From STS
conductance maps at 450 mK we observe a very disordered vortex lattice at very
low fields that melts into a vortex liquid above 3 kOe. Up to H_c^* the
tunnelling spectra display superconducting gap and coherence peak over a broad
background caused by electron-electron interactions, as expected in a vortex
liquid. However, above H_c^* the tunnelling spectra continue to display the gap
but the coherence peak gets completely suppressed, suggesting that Cooper pairs
lose their phase coherence. We conclude that H_c^* demarcates a transition from
a vortex liquid to Bose metal, that eventually transforms to a regular metal at
a higher field H* where the gap vanishes in the electronic spectrum. | 2110.09335v3 |
2021-12-18 | Infrared Absorption and its Sources of CdZnTe at Cryogenic Temperature | To reveal the infrared absorption causes in the wavelength region between
electronic and lattice absorptions, we measured the temperature dependence of
the absorption coefficient of $p$-type low-resistivity ($\sim 10^2~{\rm \Omega
cm}$) CdZnTe crystals. We measured the absorption coefficients of CdZnTe
crystals in four-wavelength bands ($\lambda=6.45$, 10.6, 11.6, 15.1$~\mu$m)
over the temperature range of $T=8.6-300$ K with an originally developed
system. The CdZnTe absorption coefficient was measured to be $\alpha=0.3-0.5$
${\rm cm^{-1}}$ at $T=300$ K and $\alpha=0.4-0.9$ ${\rm cm^{-1}}$ at $T=8.6$ K
in the investigated wavelength range. With an absorption model based on
transitions of free holes and holes trapped at an acceptor level, we conclude
that the absorption due to free holes at $T=150-300$ K and that due to
trapped-holes at $T<50$ K are dominant absorption causes in CdZnTe. We also
discuss a method to predict the CdZnTe absorption coefficient at cryogenic
temperature based on the room-temperature resistivity. | 2112.09879v1 |
2022-01-02 | Role of surface functional groups to superconductivity in Nb$_2$C-MXene: Experiments and density functional theory calculations | The recently discovered surface-group-dependent superconductivity in
Nb$_2$C-MXene fabricated by the molten salts method is attracting wide
attention. However, regarding the superconductivity of Nb$_2$C-MXene with
functional F groups (Nb$_2$CF$_x$), there were some conflicting results in
experimental and theoretical studies. Herein, we systematically carried out
experimental and theoretical investigations on the superconductivity in
Nb$_2$C-MXene with the Cl functional group (Nb$_2$CCl$_x$) and Nb$_2$CF$_x$.
The experimental results of the Meissner effect and zero resistivity have
proved that Nb$_2$CClx is superconducting with the transition temperature (Tc)
~ 5.2 K. We extract its superconducting parameters from the temperature
dependence of resistivity and the field dependence of the magnetization. The
Ginzburg-Landau parameter K$_G$$_L$ is estimated to be 2.41, indicating that
Nb$_2$CClx is a typical type-II superconductor. Conversely, both magnetic and
electrical transport measurements demonstrate that Nb$_2$CF$_x$ is not
superconducting. The first-principles density functional theory (DFT)
calculations show that the Tc of Nb$_2$Cl$_x$ is ~ 5.2 K, while Nb$_2$CF$_x$ is
dynamically unstable with imaginary frequency in phonon spectrum, which is in
good agreement with the experimental results. Our studies not only are useful
for clarifying the present inconsistency but also offer referential
significance for future investigations on the superconductivity of MXenes. | 2201.00298v1 |
2022-01-13 | Charge-Density-Wave Proximity Effects in Graphene | Certain layered transition metal dichalcogenides (TMDCs), such as 1T-TaS2,
show a rich collection of charge density wave (CDW) phases at different
temperatures, and their atomic structures and electron conductions have been
widely studied. However, the properties of CDW systems that are integrated with
other electronic materials have not yet been investigated. Here, we incorporate
the CDW properties of TMDCs into the electronic transport of graphene for the
first time. During CDW phase transitions, anomalous transport behaviors that
are closely related to the formation of correlated disorder in TMDCs were
observed in the graphene sample used in this study. In particular, the
commensurate CDW phase forms a periodic charge distribution with potential
fluctuations, and thus constitutes correlated charged impurities, which
decreases resistivity and enhances carrier mobility in graphene. The
CDW-graphene heterostructure system demonstrated here paves the way to
controlling the temperature-dependent carrier mobility and resistivity of
graphene and to developing novel functional electronic devices such as
graphene-based sensors and memory devices. | 2201.04844v2 |
2022-01-25 | Charge-4e and charge-6e flux quantization and higher charge superconductivity in kagome superconductor ring devices | The flux quantization is a key indication of electron pairing in
superconductors. For example, the well-known h/2e flux quantization is
considered strong evidence for the existence of the charge-2e, two-electron
Cooper pairs. Here we report evidence for multi-charge flux quantization in
mesoscopic ring devices fabricated using the transition-metal kagome
superconductor CsV3Sb5. We perform systematic magneto-transport measurements
and observe unprecedented quantization of magnetic flux in units of h/4e and
h/6e in magnetoresistance oscillations. Specifically, at low temperatures,
magnetoresistance oscillations with period h/2e are detected, as expected from
the flux quantization for charge-2e superconductivity. We find that the h/2e
oscillations are suppressed and replaced by resistance oscillations with h/4e
periodicity when temperature is increased. Increasing the temperature further
suppresses the h/4e oscillations and robust resistance oscillations with h/6e
periodicity emerge as evidence for charge-6e flux quantization. Our
observations provide the first experimental evidence for the existence of
multi-charge flux quanta and emergent quantum matter exhibiting higher-charge
superconductivity in the strongly fluctuating region above the charge-2e Cooper
pair condensate, revealing new insights into the intertwined and vestigial
electronic order in kagome superconductors. | 2201.10352v3 |
2022-03-09 | The drastic effect of the impurity scattering on the electronic and superconducting properties of Cu-doped FeSe | Non-magnetic impurities in iron-based superconductors can provide an
important tool to understand the pair symmetry and they can influence
significantly the transport and the superconducting behaviour. Here, we present
a study of the role of strong impurity potential in the Fe plane, induced by Cu
substitution, on the electronic and superconducting properties of single
crystals of FeSe. The addition of Cu quickly suppresses both the nematic and
superconducting states, and increases the residual resistivity due to enhanced
impurity scattering. Using magnetotransport data up to 35 T for a small amount
of Cu impurity, we detect a significant reduction in the mobility of the charge
carriers by a factor of ~3. While the electronic conduction is strongly
disrupted by Cu substitution, we identify additional signatures of anisotropic
scattering which manifest in linear resistivity at low temperatures and
$H^{1.6}$ dependence of magnetoresistance. The suppression of superconductivity
by Cu substitution is consistent with a sign-changing $s_{\pm}$ order
parameter. Additionally, in the presence of compressive strain, the
superconductivity is enhanced, similar to FeSe. | 2203.04624v1 |
2022-04-21 | Ferrous Metal Matrix Composites Status Scope and Challenges | The present paper is an effort to culminate the status, scopes and challenges
in the development of ferrous metal matrix composites (FMMCs). The FMMCs are
old but less in use than the non-ferrous metal matrix composites (NFMMCs), as
far as literature and actual applications are concerned. Therefore, this
stimulates the exploration of the reasons behind the scarcity of literature and
field applications of the FMMCs, which must be investigated scientifically. The
powder metallurgy route is the most used process for fabricating iron and steel
based FMMCs by reinforcing particulates. At the same time, the in-situ method
has been used for the fabrication and cast iron-based FMMCs. The main
characteristics being considered during the designing and fabrication of FMMCs
are wear resistance and improved specific mechanical properties. To fabricate
cheaper and eco-friendly FMMCs, traditionally used costly reinforcements such
as SiC, WC, TiC, SiO2, TiO2, TiB2 are required to be replaced by inexpensive
industrial wastes like red-mud, fly-ashes and grinding swarf. The data
extracted from the web of science exhibited that the FMMCs have been researched
less than the NFMMCs. The increasing number of research papers on FMMCs
indicates a bright future. FMMCs are going to be a favourite topic among
researchers and manufacturers. Higher strengths, wear resistance, dimensional
stability at elevated temperatures, and, most importantly, the lower cost will
put forward the FMMCs as a stiff competitor of NFMMCs. In developing and mass
production of FMMCs for field applications, challenges like oxidation and
higher weight still require special research efforts. | 2204.09999v2 |
2022-05-12 | Investigation of lattice dynamics, magnetism and electronic transport in $β$-Na$_{0.33}$V$_2$O$_{5}$ | We investigate the electronic and magnetic properties as well as lattice
dynamics and spin-phonon coupling of $\beta$-Na$_{0.33}$V$_2$O$_5$ using
temperature-dependent Raman scattering, dc-magnetization and dc-resistivity,
x-ray photoemission, and absorption spectroscopy. The Rietveld refinement of
XRD pattern with space group C2/m confirms the monoclinic structure. The
analysis of temperature-dependent Raman spectra in a temperature range of
13--673~K reveals an anharmonic dependence of the phonon frequency and full
width at half maximum, which is accredited to the symmetric phonon decay.
However, below about 40 K, the hardening of the phonon frequency beyond
anharmonicity is attributed to the spin-phonon coupling. Interestingly, the
estimated effective magnetic moment $\mu_{\rm eff}=$ 0.63~$\mu_B$ from the
magnetization data manifests a mixed-valence state of V ions in 4+ (18$\pm$1\%)
and 5+ (82$\pm$1\%). A similar ratio of V$^{4+}$ to V$^{5+}$ is also observed
in the x-ray photoemission and x-ray absorption near-edge spectra and that is
found to be consistent with the sample stoichiometry. In addition, the V$^{4+}$
ions are distributed between different vanadium (V1 and V3) sites. The analysis
of extended x-ray absorption fine structure at different V-sites gives the
corresponding V--O bond lengths, which are utilized in the assignment of Raman
modes. Moreover, the temperature-dependent resistivity resembles a
semiconducting behavior where the charge carrier transport is facilitated by
the band conduction at higher temperatures and via hopping $\le$260~K. | 2205.06019v2 |
2022-05-04 | Graphene/fluorinated graphene systems for a wide spectrum of electronics application | Heterostructures prepared from graphene and fluorographene (FG) using the
technology of 2D printing on solid and flexible substrates were fabricated and
studied. Excellent stability of printed graphene layers and, to a lesser
degree, composite graphene: PEDOT: PSS layers were shown. Extraordinary
properties of FG as an insulating layer for graphene-based heterostructures at
fluorination degree above 30% were demonstrated. It is shown that the leakage
current in thin (20-40 nm) films is normally smaller than 10^-8 A/cm2, the
breakdown field being greater than 108 V/cm. In hybrid structures with printed
FG layers in which graphene was transferred onto, or capsulated with, an FG
layer, an increase in charge-carrier mobility and material conductivity
amounting to 5-6 times was observed. The spectrum of future applications of FG
layers can be further extended due to the possibility of obtaining, from weakly
fluorinated graphene (< 20%), functional layers exhibiting a negative
differential resistance behavior and, at fluorination degrees of 20-23%,
field-effect-transistor channels with current modulation reaching several
orders. Composite or bilayer films based on fluorographene and V2O5 or
polyvinyl alcohol exhibit a stable resistive switching behavior. On the whole,
graphene/FG heterostructures enjoy huge potential for their use in a wide
spectrum of application, including flexible electronics. | 2205.07602v1 |
2022-07-14 | Magnetron Sputtered Non-Toxic and Precious Element-Free Ti-Zr-Ge Metallic Glass Nanofilms with Enhanced Biocorrosion Resistance | The chemical composition and structural state of advanced alloys are the
decisive factors in optimum biomedical performance. This contribution presents
unique Ti-Zr-Ge metallic glass thin-film compositions fabricated by magnetron
sputter deposition targeted for nanocoatings for biofouling prevention. The
amorphous nanofilms with nanoscale roughness exhibit a large relaxation and
supercooled liquid regions as revealed by flash differential scanning
calorimetry. Ti\textsubscript{68}Zr\textsubscript{8}Ge\textsubscript{24} shows
the lowest corrosion (0.17 \textmu A cm\textsuperscript{\textminus2}) and
passivation (1.22 \textmu A cm\textsuperscript{\textminus2}) current densities,
with the lowest corrosion potential of \textminus0.648 V and long-range
stability against pitting, corroborating its excellent performance in phosphate
buffer solution at 37 {\textdegree}C. The oxide layer is comprised of
TiO\textsubscript{2}, TiO\textsubscript{\emph{x}} and
ZrO\textsubscript{\emph{x}}, as determined using X-ray photoelectron
spectroscopy by short-term ion-etching of the surface layer. The two orders of
magnitude increase in the oxide and interface resistance (from 14 to 1257
{\textOmega} cm\textsuperscript{2}) along with an order of magnitude decrease
in the capacitance parameter of the oxide interface (from 1.402 x
10\textsuperscript{\textminus5} to 1.677 x 10\textsuperscript{\textminus6} S
s\textsuperscript{n} cm\textsuperscript{\textminus2}) of the same composition
is linked to the formation of carbonyl groups and reduction of the native oxide
layer during linear sweep voltammetry. | 2207.07000v2 |
2022-08-09 | Structural, magnetic and transport properties of Co$_2$CrAl epitaxial thin films | We report the physical properties of Co$_2$CrAl Heusler alloy epitaxial thin
films grown on single crystalline MgO(001) substrate using pulsed laser
deposition technique. The x-ray diffraction pattern in $\theta$-2$\theta$ mode
showed the film growth in single phase B2-type ordered cubic structure with the
presence of (002) and (004) peaks, and the film oriented along the MgO(001)
direction. The $\phi$~scan along the (220) plane confirms the four-fold
symmetry and the epitaxial growth relation found to be
Co$_2$CrAl(001)[100]$\vert$$\vert$MgO(001)[110]. The thickness of about 12~nm
is extracted through the analysis of x-ray reflectivity data. The isothermal
magnetization (M--H) curves confirm the ferromagnetic (FM) nature of the thin
film having significant hysteresis at 5 and 300~K. From the in-plane M--H
curves, the saturation magnetization values are determined to be
2.1~$\mu$$_{\rm B}$/f.u.~at 5~K and 1.6~$\mu$$_{\rm B}$/f.u. at 300~K, which
suggests the soft FM behavior in the film having the coercive field $\approx$
522~Oe at 5~K. The thermo-magnetization measurements at 500~Oe magnetic field
show the bifurcation between field-cooled and zero-field-cooled curves below
about 100~K. The normalized field-cooled magnetization curve follows the T$^2$
dependency, and the analysis reveal the Curie temperature around 335$\pm$11~K.
Moreover, the low-temperature resistivity indicates semiconducting behavior
with the temperature, and we find a negative temperature coefficient of
resistivity (5.2 $\times$ 10$^{-4}$ /K). | 2208.04687v1 |
2022-10-21 | Effect of Pressure on Electrical and optical Properties of Metal Doped TiO$_2$ | A comparative study of the electrical and optical properties has been done on
3d-doped TiO$_2$. Ti$_{1-x}$M$_x$O$_2$ (M= Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn)
powder and its corresponding pellets, with doping concentration $x= 0.05$. The
samples were prepared using the solid-state route. Optical and electrical
measurements have been performed for all prepared samples and interestingly, it
is observed that due to external pressure (i.e. strain) both the properties
change significantly. A rigorous theoretical calculation has also been carried
out to verify the experimental band gap obtained from optical absorption
spectroscopy. In case of pellet sample band gap decreases as compared to the
powder sample due to variation of pressure inside the structures. Role of
doping has also been investigated both in pellet and powder forms and we found
that the band gap decreases as the atomic number of dopants increases. A
cross-over behavior is seen in pellet samples on doping with Ni, Cu and Zn
(i.e. band gap increases with an increase in the atomic number of dopant).
Electrical resistivity measurements have been carried out for both pellet and
powder samples and it is found that in the case of strained samples the value
of resistivity is smaller while in the case of strain-free samples it is quite
large. We believe that the present study suggests a novel approach for tuning
the electrical and optical properties of semiconducting oxides either from
doping or from applied pressure (or strain). | 2210.11687v1 |
2022-10-28 | Optimal Inverter-Based Resources Placement in Low-Inertia Power Systems | An increase in the integration of Inverter Based Resources (IBRs) to the
electric grid, will lead to a corresponding decrease in the amount of connected
synchronous generators, resulting in a decline in the available rotational
inertia system-wide. This can lead to pronounced frequency deviations when
there are disturbances and faults in the grid. This decline in available
rotational inertia can be compensated for by fast acting IBRs participating in
frequency response services, by rapidly injecting into or removing power from
the grid. Currently, there are still relative small number of sizable IBRs in
the grid. Therefore, the placement of the IBRs in the system, as well as the
inverter configuration type and controller, will have a material impact on the
frequency response of the grid. In this work, we present an optimal placement
algorithm that maximizes the benefits of utilizing IBRs in providing frequency
response services. That is, we minimize the overall system frequency deviation
while using a minimal amount of electric power injection from the IBRs. The
proposed algorithm uses the resistance distance to place the IBRs at nodes that
are central to the rest of the nodes in the network thus minimizing the
distance of power flow. The proposed greedy algorithm achieves a near optimal
performance and relies on the supermodularity of the resistance distances. We
validate the performance of the placement algorithm on three IEEE test systems
of varying sizes, by comparing its performance to an exhaustive search
algorithm. We further evaluate the performance of the placed IBRs on an IEEE
test system, to determine their impact on frequency stability. The IBRs are
configured in a grid-forming mode and equipped with a model predictive control
(MPC)-based inverter power control. | 2210.15839v1 |
2022-12-16 | Environmental Doping-Induced Degradation of the Quantum Anomalous Hall Insulators | The quantum anomalous Hall (QAH) insulator is a topological quantum state
with quantized Hall resistance and zero longitudinal resistance in the absence
of an external magnetic field. The QAH insulator carries spin-polarized
dissipation-free chiral edge current and thus provides a unique opportunity to
develop energy-efficient transformative information technology. Despite
promising advances on the QAH effect over the past decade, the QAH insulator
has thus far eluded any practical applications. In addition to its low working
temperature, the QAH state in magnetically doped topological insulator (TI)
films/heterostructures usually deteriorates with time in ambient conditions. In
this work, we prepare three QAH devices with similar initial properties and
store them in different environments to investigate the evolution of their
transport properties. The QAH device without a protection layer in air show
clear degradation and becomes hole-doped with the charge neutral point shifting
significantly to positive gate voltages. The QAH device kept in an argon glove
box without a protection layer shows no measurable degradation after 560 hours
and the device protected by a 3 nm AlOx protection layer in air shows minimal
degradation with stable QAH properties. Our work shows a route to preserve the
dissipation-free chiral edge state in QAH devices for potential applications in
quantum information technology. | 2212.08538v1 |
2023-01-13 | Exploring the substrate-driven morphological changes in Nd0.6Sr0.4MnO3 thin films | Manganite thin films are promising candidates for studying the strongly
correlated electron systems. Understanding the growth-and morphology-driven
changes in the physical properties of manganite thin films is vital for their
applications in oxitronics. This work reports the morphological, structural,
and electrical transport properties of nanostructured Nd0.6Sr0.4MnO3 (NSMO)
thin films fabricated using the pulsed laser deposition technique. Scanning
electron microscopy (SEM) imaging of the thin films revealed two prominent
surface morphologies: a granular and a unique crossed-nano-rod-type morphology.
From X-ray diffraction (XRD) and atomic force microscopy (AFM) analysis, we
found that the observed nanostructures resulted from altered growth modes
occurring on the terraced substrate surface. Furthermore, investigations on the
electrical-transport properties of thin films revealed that the films with
crossed-nano-rod type morphology showed a sharp resistive transition near the
metal-to-insulator transition (MIT). An enhanced temperature coefficient of
resistance (TCR) of up to one order of magnitude was also observed compared to
the films with granular morphology. Such enhancement in TCR % by tuning the
morphology makes these thin films promising candidates for developing
oxide-based temperature sensors and detectors. | 2301.05513v1 |
2023-01-30 | Percolation and electrical conduction in random systems of curved linear objects on a plane: computer simulations along with a mean-field approach | Using computer simulations, we have studied the percolation and the
electrical conductance of two-dimensional, random percolating networks of
curved, zero-width metallic nanowires. We mimicked the curved nanowires using
circular arcs. The percolation threshold decreased as the aspect ratio of the
arcs increased. Comparison with published data on the percolation threshold of
symmetric quadratic B\'{e}zier curves suggests that, when the percolation of
slightly curved wires is simulated, the particular choice of curve to mimic the
shape of real-world wires is of little importance. Considering the electrical
properties, we took into account both the nanowire resistance per unit length
and the junction (nanowire/nanowire contact) resistance. Using a mean-field
approximation (MFA), we derived the total electrical conductance of the
nanowire-based networks as a function of their geometrical and physical
parameters. The MFA predictions have been confirmed by our Monte Carlo
numerical simulations. For our random homogeneous and isotropic systems of
conductive curved wires, the electric conductance decreased as the wire shape
changed from a stick to a ring when the wire length remained fixed. | 2301.12795v1 |
2023-01-31 | Platinum contacts for 9-atom-wide armchair graphene nanoribbons | Creating a good contact between electrodes and graphene nanoribbons (GNRs)
has been a longstanding challenge in searching for the next GNR-based
nanoelectronics. This quest requires the controlled fabrication of sub-20 nm
metallic gaps, a clean GNR transfer minimizing damage and organic contamination
during the device fabrication, as well as work function matching to minimize
the contact resistance. Here, we transfer 9-atom-wide armchair-edged GNRs
(9-AGNRs) grown on Au(111)/mica substrates to pre-patterned platinum
electrodes, yielding polymer-free 9-AGNR field-effect transistor devices. Our
devices have a resistance in the range of $10^6$ to $10^8$ $\Omega$ in the
low-bias regime, which is 2 to 4 orders of magnitude lower than previous
reports. Density functional theory (DFT) calculations combined with the
non-equilibrium Green's function method (NEGF) explain the observed p-type
electrical characteristics and further demonstrate that platinum gives strong
coupling and higher transmission in comparison to other materials such as
graphene. | 2301.13814v1 |
2023-02-13 | Growth of Zr/ZrO2 core-shell structures by Fast Thermal Oxidation | This research has been conducted to characterize and validate the resistive
heating as a synthesis method for zirconium oxides (ZrO$_2$). A wire of Zr has
been oxidized to form a core shell structure, in which the core is the metal
wire, and the shell is an oxide layer around 10${\mu}$m thick. The
characterization This research has been conducted to characterize and validate
the resistive heating as a synthesis method for zirconium oxides (ZrO$_2$). A
wire of Zr has been oxidized to form a core shell structure, in which the core
is the metal wire, and the shell is an oxide layer around 10${\mu}$m thick. The
characterization of the samples has been performed by means of Scanning
Electron Microscopy (SEM). The chemical composition was analysed by X-ray
spectroscopy (EDX). X-ray diffraction (XRD) and Raman spectroscopy have been
used to assess crystallinity and crystal structure. Photoluminescence (PL) and
cathodoluminescence (CL) measurements have allowed us to study the distribution
of defects along the shell, and to confirm the degree of uniformity. The oxygen
vacancies, either as isolated defects or forming complexes with impurities,
play a determinant role in the luminescent processes. Colour centres, mainly
electron centres as F, F$_A$ and F$_{AA}$, give rise to several visible
emissions extending from blue to green, with main components around 2eV,
2.4-2.5eV and 2.7eV. The differences between PL and CL are also discussed. | 2302.06296v1 |
2023-03-15 | Magnetic phase diagram and multiple field-induced states in the intermetallic triangular-lattice antiferromagnet NdAuAl$_4$Ge$_2$ with Ising-like spins | Geometrical frustration and the enhancement of strong quantum fluctuations in
two-dimensional triangular antiferromagnets can lead to various intriguing
phenomena. Here, we studied the spin-1/2 triangular lattice antiferromagnet
NdAuAl$_4$Ge$_2$. Thermodynamic and transport properties, such as magnetization
and specific heat together with the resistivity measurements were performed. In
zero field, two successive phase transitions were observed at $T_{\rm
N1}=1.75\pm 0.02$ K and $T_{\rm N2}=0.49\pm 0.02$ K, respectively. Under
magnetic field, $\rm XXZ$-type anisotropy was revealed, with the moments
pointing along the easy $c$ axis. For $B\parallel c$, multiple field-induced
states were observed, and the magnetic phase diagram was established based on
the specific heat and magnetization data. The temperature-dependent resistivity
measurements indicate that NdAuAl$_4$Ge$_2$ is a good metal. It is very likely
that both the long-range RKKY interactions and the geometrical frustration play
an important roles in this case. | 2303.08661v1 |
2023-04-07 | Effect of Pt vacancies on magnetotransport of Weyl semimetal candidate GdPtSb epitaxial films | We examine the effects of Pt vacancies on the magnetotransport properties of
Weyl semimetal candidate GdPtSb films, grown by molecular beam epitaxy on
c-plane sapphire. Rutherford backscattering spectrometry (RBS) and x-ray
diffraction measurements suggest that phase pure GdPt$_{x}$Sb films can
accommodate up to $15\%$ Pt vacancies ($x=0.85$), which act as acceptors as
measured by Hall effect. Two classes of electrical transport behavior are
observed. Pt-deficient films display a metallic temperature dependent
resistivity (d$\rho$/dT$>$0). The longitudinal magnetoresistance (LMR, magnetic
field $\mathbf{B}$ parallel to electric field $\mathbf{E}$) is more negative
than transverse magnetoresistance (TMR, $\mathbf{B} \perp \mathbf{E}$),
consistent with the expected chiral anomaly for a Weyl semimetal. The
combination of Pt-vacancy disorder and doping away from the expected Weyl
nodes; however, suggests conductivity fluctuations may explain the negative LMR
rather than chiral anomaly. Samples closer to stoichiometry display the
opposite behavior: semiconductor-like resistivity (d$\rho$/dT$<$0) and more
negative transverse magnetoresistance than longitudinal magnetoresistance.
Hysteresis and other nonlinearities in the low field Hall effect and
magnetoresistance suggest that spin disorder scattering, and possible
topological Hall effect, may dominate the near stoichiometric samples. Our
findings highlight the complications of transport-based identification of Weyl
nodes, but point to possible topological spin textures in GdPtSb. | 2304.03811v1 |
2023-05-22 | Development of Fe$_2$O$_3$/YSZ ceramic plates for cryogenic operation of resistive-protected gaseous detectors | We present a ceramic material based on hematite (Fe$_2$O$_3$) and zirconia
stabilized with yttria at 8% molar (YSZ), that exhibits stable electrical
properties with transported charge and that can be tuned to the resistivities
necessary to induce spark-quenching in gaseous detectors ($\rho = 10^9-10^{12}$
$\Omega \cdot$cm), from room temperature down to the liquid-vapor coexistence
point of nitrogen (77 K). It, thus, allows covering the operating temperatures
of most immediate interest to gaseous instrumentation. The ceramics have been
produced in a region of mass concentrations far from what has been usually
explored in literature: optimal characteristics are achieved for Fe$_2$O$_3$
concentrations of 75%wt (LAr boiling temperature), 35%wt (LXe boiling
temperature), and 100%wt (room temperature). The nine order of magnitude
enhancement observed for the electrical conductivity of the mixed phases
relative to that of pure Fe$_2$O$_3$ is startling, however it can be
qualitatively understood based on existing literature. Plates of 4 cm x 4 cm
have been manufactured and, prior to this work, operated in-detector at the LXe
boiling point (165 K), demonstrating spark-free operation. Preliminary results
obtained for the first time on a spark-protected amplification structure
(RP-WELL) at around the LAr boiling point (90 K) are now presented, too. | 2305.12899v2 |
2023-07-05 | An efficient approach to include transport effects in thin coating layers in electrochemo-mechanical models for all-solid-state batteries | A novel approach is presented to efficiently include transport effects in
thin active material coating layers of all-solid-state batteries using a
dimensionally reduced formulation embedded into a three-dimensionally resolved
coupled electrochemo-mechanical continuum model. In the literature, the effect
of coating layers is so far captured by additional zero-dimensional resistances
to circumvent the need for an extremely fine mesh resolution. However, a
zero-dimensional resistance cannot capture transport phenomena along the
coating layer, which can become significant, as we will show in this work.
Thus, we propose a model which resolves the thin coating layer in a
two-dimensional manifold based on model assumptions in the direction of the
thickness. This two-dimensional formulation is monolithically coupled with a
three-dimensional model representing the other components of a battery cell.
The approach is validated by showing conservation properties and convergence
and by comparing the results with those computed with a fully resolved model.
Results for realistic microstructures of a battery cell, including coating
layers as well as design recommendations for a preferred coating layer, are
presented. Based on those results, we show that existing modeling approaches
feature remarkable errors when transport along the coating layer is
significant, whereas the novel approach resolves this. | 2307.02424v1 |
2023-08-04 | Effect of Pb addition on microstructure, transport properties and the critical current density in a polycrystalline FeSe0.5Te0.5 | We have investigated the effects of lead (Pb) additions (x) up to 40 wt.% (x
= 0-0.4) on the structure, electrical properties, and magnetic properties of
FeSe0.5Te0.5 superconductor. The samples were prepared by the solid-state
reaction method and characterized by various techniques. The parent compound (x
= 0) showed the onset temperature Tc onset of 15 K, and zero-resistance
temperature, Tc offset of 12 K. The addition of Pb enhances the metallic
characteristics of FeSe0.5Te0.5, but both Tc onset and Tc offset are decreased
to the lower temperature with the broadened transition width. The Tc onset is
nearly the same (10.3 K) at higher additions, such as x = 0.3 and 0.4, but zero
resistivity is not observed up to 7 K. Microstructural analysis and transport
studies suggest that for x > 0.05, Pb additions weakened the coupling between
grains and suppressed the superconducting percolation, leading to a broad
transition. More importantly, the inclusion of a relatively small amount of Pb
(x = 0.05) increased the critical current density, Jc, in the entire magnetic
field, which might be attributable to better phase uniformity as well as good
grain connectivity. | 2308.02128v1 |
2023-08-07 | Single crystal growth and characterization of antiferromagnetically ordering EuIn$_2$ | We report the single crystal growth and characterization of EuIn$_2$, a
magnetic topological semimetal candidate according to our density functional
theory (DFT) calculations. We present results from electrical resistance,
magnetization, M\"ossbauer spectroscopy, and X-ray resonant magnetic scattering
(XRMS) measurements. We observe three magnetic transitions at
$T_{\text{N}1}\sim 14.2~$K, $T_{\text{N}2}\sim12.8~$K and $T_{\text{N}3}\sim
11~$K, signatures of which are consistently seen in anisotropic temperature
dependent magnetic susceptibility and electrical resistance data. M\"ossbauer
spectroscopy measurements on ground crystals suggest an incommensurate
sinusoidally modulated magnetic structure below the transition at
$T_{\text{N}1}\sim 14~$K, followed by the appearance of higher harmonics in the
modulation on further cooling roughly below $T_{\text{N}2}\sim13~$K, before the
moment distribution squaring up below the lowest transition around
$T_{\text{N}3}\sim 11~$K. XRMS measurements showed the appearance of magnetic
Bragg peaks below $T_{\text{N}1}\sim14~$K, with a propagation vector of
$\bm{\tau}$ $=(\tau_h,\bar{\tau}_h,0)$, with $\tau_h$varying with temperature,
and showing a jump at $T_{\text{N}3}\sim11$~K. The temperature dependence of
$\tau_h$ between $\sim11$~K and $14$~K shows incommensurate values consistent
with the M\"{o}ssbauer data. XRMS data indicate that $\tau_h$ remains
incommensurate at low temperatures and locks into $\tau_h=0.3443(1)$. | 2308.03600v1 |
2023-08-10 | Ferromagnetism and insulating behavior with a logarithmic temperature dependence of resistivity in $Pb_{10-x}Cu_x\left( PO_4 \right) _6O$ | Recent claim of discovering above-room-temperature superconductivity (Tc
about 400 K) at ambient pressure in copper doped apatite $Pb_{10}\left( PO_4
\right) _6O$ has stimulated world-wide enthusiasm and impulse of motion. A lot
of follow-up works have been carried out with controversial conclusions. To
check whether superconductivity is really present or absent in the material, we
need samples which should have a rather pure phase of $Pb_{10-x}Cu_x\left( PO_4
\right) _6O$. Here we report the characterization results from the
$Pb_{10-x}Cu_x\left( PO_4 \right) _6O$ with a fraction of about 97 wt.%
inferred from the fitting to the x-ray diffraction pattern. The resistivity
measurements show that it is a semiconductor characterized roughly by a ln(1/T)
temperature dependence in wide temperature region without trace of
superconductivity. Magnetization measurements show that it has a general
ferromagnetic signal with a weak superparamagnetic background. Many grains of
the sample show clear interactions with a NbFeB magnet. The detected Cu
concentration is much lower than the expected nominal one and the conduction
may be improved if more Cu atoms are successfully doped into the system. Our
results show the absence of metallicity and superconductivity in
$Pb_{10-x}Cu_x\left( PO_4 \right) _6O$ at ambient pressure, and suggest the
presence of strong correlation effect. | 2308.05786v3 |
2023-08-15 | Thermoelectric response across the semiconductor-semimetal transition in black phosphorus | In spite of intensive studies on thermoelectricity in metals, little is known
about thermoelectric response in semiconductors at low temperature. An even
more fascinating and unanswered question is what happens to the Seebeck
coefficient when the semiconductor turns to a metal. By precisely tuning the
ground state of black phosphorus with pressure from the semiconducting to
semimetallic state, we track a systematic evolution of the Seebeck coefficient.
Thanks to a manifest correlation between the Seebeck coefficient and
resistivity, the Seebeck response in each conduction regime, i.e., intrinsic,
saturation, extrinsic, and variable range hopping (VRH) regimes, is identified.
In the former two regimes, the Seebeck coefficient behaves in accordance with
the present theories, whereas in the later two regimes available theories do
not give a satisfactory account for its response. However, by eliminating the
extrinsic sample dependence in the resistivity $\rho$ and Seebeck coefficient
$S$, the Peltier conductivity $\alpha=S/\rho$ allows to unveil the intrinsic
thermoelectric response, revealing vanishing fate for $\alpha$ in the VRH
regime. The emerged ionized impurity scattering on entry to the semimetallic
state is easily surpassed by electron-electron scattering due to squeezing of
screening length accompanied by an increase of carrier density with pressure.
In the low temperature limit, a small number of carriers enhances a prefactor
of $T$-linear Seebeck coefficient as large as what is observed in prototypical
semimetals. A crucial but largely ignored role of carrier scattering in
determining the magnitude and sign of the Seebeck coefficient is indicated by
the observation that a sign reversal of the $T$-linear prefactor is concomitant
with a change in dominant scattering mechanism for carriers. | 2308.07900v1 |
2023-08-18 | Anomalous Hall effect induced by Berry curvature in topological nodal-line van der Waals ferromagnet Fe$_4$GeTe$_2$ | The exploration of nontrivial transport phenomena associated with the
interplay between magnetic order and spin-orbit coupling (SOC), particularly in
van der Waals (vdW) systems has gained a resurgence of interest due to their
easy exfoliation, ideal for two-dimensional (2D) spintronics. We report the
near room temperature quasi-2D ferromagnet, Fe$_4$GeTe$_2$ from the iron-based
vdW family (Fe$_n$GeTe$_2$, $n$=3,4,5), exhibiting a large anomalous Hall
conductivity (AHC), $\sigma^A_{xy}$ $\sim$ 490 $\Omega^{-1}\textrm{cm}^{-1}$ at
2 K. The near quadratic behavior of anomalous Hall resistivity
($\rho^{A}_{xy}$) with the longitudinal resistivity ($\rho_{xx}$) suggests that
a dominant AHC contribution is coming from an intrinsic Berry curvature (BC)
mechanism. Concomitantly, the electronic structure calculations reveal a large
BC arising from SOC induced gaped nodal lines around the Fermi level, governing
such large AHC property. Moreover, we also report an exceptionally large
anomalous Hall angle ($\simeq$ 10.6\%) and Hall factor ($\simeq$ 0.22 V$^{-1}$)
values which so far, are the largest in compared to those for other members in
this vdW family. | 2308.09695v1 |
2023-08-25 | Evidence of the Coulomb gap in the density of states of MoS$_2$ | $\mathrm{MoS_2}$ is an emergent van der Waals material that shows promising
prospects in semiconductor industry and optoelectronic applications. However,
its electronic properties are not yet fully understood. In particular, the
nature of the insulating state at low carrier density deserves further
investigation, as it is important for fundamental research and applications. In
this study, we investigate the insulating state of a dual-gated exfoliated
bilayer $\mathrm{MoS_2}$ field-effect transistor by performing magnetotransport
experiments. We observe positive and non-saturating magnetoresistance, in a
regime where only one band contributes to electron transport. At low electron
density ($\sim 1.4\times 10^{12}~\mathrm{cm^{-2}}$) and a perpendicular
magnetic field of 7 Tesla, the resistance exceeds by more than one order of
magnitude the zero field resistance and exponentially drops with increasing
temperature. We attribute this observation to strong electron localization.
Both temperature and magnetic field dependence can, at least qualitatively, be
described by the Efros-Shklovskii law, predicting the formation of a Coulomb
gap in the density of states due to Coulomb interactions. However, the
localization length obtained from fitting the temperature dependence exceeds by
more than one order of magnitude the one obtained from the magnetic field
dependence. We attribute this discrepancy to the presence of a nearby metallic
gate, which provides electrostatic screening and thus reduces long-range
Coulomb interactions. The result of our study suggests that the insulating
state of $\mathrm{MoS_2}$ originates from a combination of disorder-driven
electron localization and Coulomb interactions. | 2308.13337v2 |
2023-09-05 | Localized f-electron magnetism in the semimetal Ce3Bi4Au3 | Ce$_{3}$Bi$_{4}$Au$_{3}$ crystallizes in the same non-centrosymmetric cubic
structure as the prototypical Kondo insulator Ce$_{3}$Bi$_{4}$Pt$_{3}$. Here we
report the physical properties of Ce$_{3}$Bi$_{4}$Au$_{3}$ single crystals
using magnetization, thermodynamic, and electrical-transport measurements.
Magnetic-susceptibility and heat-capacity data reveal antiferromagnetic (AFM)
order below $T_N=3.2$ K. The magnetic entropy $S_{\rm mag}$ reaches $R$ln2
slightly above $T_N$, which suggests localized $4f$-moments in a doublet ground
state. Multiple field-induced magnetic transitions are observed at temperatures
below $T_N$, which indicate a complex spin structure with competing
interactions. Ce$_{3}$Bi$_{4}$Au$_{3}$ shows semimetallic behavior in
electrical resistivity measurements in contrast to the majority of reported
Cerium-based 343 compounds. Electrical-resistivity measurements under
hydrostatic pressure reveal a slight enhancement of $T_N$ under pressures up to
2.3 GPa, which supports a scenario wherein Ce$_{3}$Bi$_{4}$Au$_{3}$ belongs to
the far left of the Doniach phase diagram dominated by
Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. Using realistic many-body
simulations, we confirm the semi-metallic electronic structure of
Ce$_{3}$Bi$_{4}$Au$_{3}$ and quantitatively reproduce its local moment behavior
in the paramagnetic state. | 2309.02559v1 |
2023-09-27 | Design of Passive and Structural Conductors for Tokamaks Using Thin-Wall Eddy Current Modeling | A new three-dimensional electromagnetic modeling tool ThinCurr has been
developed using the existing PSI-Tet finite-element code in support of
conducting structure design work for both the SPARC and DIII-D tokamaks. Within
this framework a 3D conducting structure model was created for both the SPARC
and DIII-D tokamaks in the thin-wall limit. This model includes accurate
details of the vacuum vessel and other conducting structural elements with
realistic material resistivities. This model was leveraged to support the
design of a passive runaway electron mitigation coil (REMC), studying the
effect of various design parameters, including coil resistivity, current quench
duration, and plasma vertical position, on the effectiveness of the coil. The
REMC is a non-axisymmetric coil designed to passively drive large
non-axisymmetric fields during the plasma disruption thereby destroying flux
surfaces and deconfining RE seed populations. These studies indicate that
current designs should apply substantial 3D fields at the plasma surface during
future plasma current disruptions as well as highlight the importance of having
the REMC conductors away from the machine midplane in order to ensure they are
robust to off-normal disruption scenarios. | 2309.15336v1 |
2023-10-02 | Dielectric Detection of Single Nanoparticles Using a Microwave Resonator Integrated with a Nanopore | The characterization of individual nanoparticles in a liquid constitutes a
critical challenge for environmental, material, and biological sciences. To
detect nanoparticles, electronic approaches are especially desirable owing to
their compactness and lower costs. Indeed, for single-molecule and
single-nanoparticle detection, resistive pulse sensing has advanced
significantly during the last two decades. While resistive pulse sensing was
widely used to obtain the geometric size information, impedimetric measurements
to obtain dielectric signatures of nanoparticles have scarcely been reported.
To explore this orthogonal sensing modality, we developed an impedimetric
sensor based on a microwave resonator with a nanoscale sensing gap surrounding
a nanopore. The approach of single nanoparticles near the sensing region and
their translocation through the nanopore induced sudden changes in the
impedance of the structure. The impedance changes in turn were picked up by the
phase response of the microwave resonator. We worked with 100 nm and 50 nm
polystyrene nanoparticles to observe single-particle events. Our current
implementation was limited by the non-uniform electric field at the sensing
region. The work provides a complementary sensing modality for nanoparticle
characterization where the dielectric response, rather than the ionic current,
determines the signal. | 2310.00910v1 |
2023-10-16 | Growth and characterization of the magnetic topological insulator candidate Mn$_2$Sb$_2$Te$_5$ | We report a new member of topological insulator (TI) family i.e.,
Mn$_2$Sb$_2$Te$_5$, which belongs to MnSb$_2$Te$_4$ family and is a sister
compound of Mn$_2$Bi$_2$Te$_5$. An antiferromagnetic layer of (MnTe)$_2$ has
been inserted between quintuple layers of Sb$_2$Te$_3$. The crystal structure
and chemical composition of as grown Mn$_2$Sb$_2$Te$_5$ crystal is
experimentally visualized by single crystal XRD (SCXRD) and field emission
scanning electron microscopy (FESEM). The valence states of individual
constituents i.e., Mn, Sb and Te are ascertained through X ray photo electron
spectroscopy (XPS). Different vibrational modes of Mn$_2$Sb$_2$Te$_5$ are
elucidated through Raman spectroscopy. Temperature-dependent resistivity of
Mn$_2$Sb$_2$Te$_5$ resulted in metallic behaviour of the same with an up-turn
at below around 20K. Further, the magneto-transport R(T) vs H of the same
exhibited negative magneto-resistance (MR) at low temperatures below 20K and
small positive at higher temperatures. The low Temperature -ve MR starts
decreasing at higher fields. The magnetic moment as a function of temperature
at 100Oe and 1kOe showed AFM like down turn cusps at around 20K and 10K. The
isothermal magnetization (MH) showed AFM like loops with some embedded FM/PM
domains at 5K and purely paramagnetic (PM) like at 100K. The studied
Mn$_2$Sb$_2$Te$_5$ clearly exhibited the characteristics of a magnetic TI
(MTI). | 2310.10163v1 |
2023-10-22 | Investigation of the mechanism of the anomalous Hall effects in Cr2Te3/(BiSb)2(TeSe)3 heterostructure | The interplay between ferromagnetism and the non-trivial topology has
unveiled intriguing phases in the transport of charges and spins. For example,
it is consistently observed the so-called topological Hall effect (THE)
featuring a hump structure in the curve of the Hall resistance (Rxy) vs. a
magnetic field (H) of a heterostructure consisting of a ferromagnet (FM) and a
topological insulator (TI). The origin of the hump structure is still
controversial between the topological Hall effect model and the multi-component
anomalous Hall effect (AHE) model. In this work, we have investigated a
heterostructure consisting of BixSb2-xTeySe3-y (BSTS) and Cr2Te3 (CT), which
are well-known TI and two-dimensional FM, respectively. By using the so-called
minor-loop measurement, we have found that the hump structure observed in the
CT/BSTS is more likely to originate from two AHE channels. Moreover, by
analyzing the scaling behavior of each amplitude of two AHE with the
longitudinal resistivities of CT and BSTS, we have found that one AHE is
attributed to the extrinsic contribution of CT while the other is due to the
intrinsic contribution of BSTS. It implies that the proximity-induced
ferromagnetic layer inside BSTS serves as a source of the intrinsic AHE,
resulting in the hump structure explained by the two AHE model. | 2310.14259v1 |
2023-11-09 | Lithium-ion battery degradation: using degradation mode analysis to validate lifetime prediction modelling | Predicting lithium-ion battery lifetime is one of the greatest unsolved
problems in battery research right now. Recent years have witnessed a surge in
lifetime prediction papers using physics-based, empirical, or data-driven
models, most of which have been validated against the remaining capacity
(capacity fade) and sometimes resistance (power fade). However, there are many
different combinations of degradation mechanisms in lithium-ion batteries that
can result in the same patterns of capacity and power fade, making it
impossible to find a unique validated solution. Experimentally, degradation
mode analysis involving measuring the loss of lithium inventory, loss of active
material at both electrodes, and electrode drift/slippage has emerged as a
state-of-the-art requirement for cell degradation studies. In this paper we
coupled five degradation mechanisms together for the first time. We also showed
how three models with different levels of complexity can all fit the remaining
capacity and resistance well, but only the model with five coupled degradation
mechanisms could also fit the degradation modes at all temperatures. This work
proves that validating only against capacity and power fade is no longer
sufficient, and state-of-the-art experimental and modelling degradation studies
should include degradation mode analysis for validation in the future. | 2311.05482v2 |
2023-11-19 | Non-Hermitian effect to the ballistic transport and quantized Hall conductivity in 2H-MoS$_{2}$ | By designing a multi-channel millimeter Hall measurement configuration, we
realize the carrier-density (locally) controllable measurement on the transport
property in 2H MoS$_{2}$. We observe a linearly increased Hall conductivity and
exponentially decreased resistivity as the increase of dc current. The
intrinsically large band gap does not exhibit too much effect on our
measurement, as far as the magnetic field is above the critical value, which is
$B=6$ T for 2H-MoS$_{2}$. Instead, the edge effect which emerge as a result of
one-dimensional channels. This is different from the Corbino geometry which is
widely applied on semiconductors, where the edges are absent. At room
temperature, we observe that the emergent quantized quantum Hall plateaus are
at the same value for both the two measurements, which implies that the
quantized conductivity does not depends on the non-Hermitian interactions, but
the number of partially filled Landau levels, and this is in consistent with
the previous theoretical works\cite{Siddiki}. At low-temperature limit, the
Hall plateaus are destroyed due to the filtered contribution from the electrons
above fermi energy, and in this case, the two measuremens exhibits stronger
distinction, where we observe stronger fluctuations (of voltage, conductivity,
and resistivity) at the currents between where there are Hall plateaus at
higher temperature. | 2311.11276v3 |
2023-11-24 | Even-in-magnetic-field part of transverse resistivity as a probe of magnetic order | The detection of a voltage transverse to both an applied current and a
magnetic field is one of the most common characterization techniques in
solid-state physics. The corresponding component of the resistivity tensor
$\rho_{ij}$ can be separated into odd and even parts with respect to the
applied magnetic field. The former contains information, for example, about the
ordinary or anomalous Hall effect. The latter is typically ascribed to
experimental artefacts and ignored. We here show that upon suppressing these
artefacts in carefully controlled experiments, useful information remains. We
first investigate the well-explored ferromagnet CoFeB, where the even part of
$\rho_{yx}$ contains a contribution from the anisotropic magnetoresistance,
which we confirm by Stoner-Wohlfarth modelling. We then apply our approach to
magnetotransport measurements in $\rm Mn_5Si_3$ thin films with a complex
compensated magnetic order. In this material, the even part of the transverse
signal is sizable only in the low-spin-symmetry phase below $\approx 80$ K and
thus offers a simple and readily available probe of the magnetic order. | 2311.14498v1 |
2023-12-10 | Radiation resistance of fine-grained ceramics Y2.5Nd0.5Al5O12 under Xe-ions irradiation | Oxide Y2.5Nd0.5Al5O12 (YAG:Nd) with garnet structure was synthesized in the
powder and ceramics forms. Fine-grained YAG:Nd ceramics with a relative density
of ~99% were obtained by the Spark Plasma Sintering method (SPS). The radiation
resistance of ceramics was studied under irradiation with swift Xe-ions (E =
146 MeV). A gradient defect structure is formed in irradiated ceramics, varying
from layer to layer. The strained YAG phase formed as a result of Xe ions
irradiation is localized in a near-surface layer with a thickness of ~5 {\mu}m.
Full amorphization of the samples was observed under irradiation with a fluence
of 1x10^13 cm-2. The calculated critical fluence was 6.5x10^12 cm-2, which
corresponded to 0.03 dpa. The microhardness of the surface layers of irradiated
ceramics is less than the central layers, and, in general, decreases with
increasing ion fluence. | 2312.05820v1 |
2024-01-16 | Thermoelectric power of overdoped Tl2201 crystals: Charge density waves and $T^1$ and $T^2$ resistivities | We report measurements of the in-plane thermoelectric power (TEP) for an
overdoped (OD) crystal of the single layer cuprate superconductor
Tl$_2$Ba$_2$CuO$_{6+x}$ (Tl2201) at several hole concentrations ($p$), from 300
or 400 K to below the superconducting transition temperature ($T_c$). For $p$ =
0.192 and 0.220, small upturns in the TEP below 150 K are attributed to the
presence of charge density waves (CDW) detected by resonant inelastic X-ray
scattering studies. This suggests that measurement of the TEP could provide a
simple and effective guide to the presence of a CDW. Over a certain temperature
range, often strongly restricted by the CDW, the TEP is consistent with the
Nordheim-Gorter rule and the $T^1$ and $T^2$ terms in the in-plane resistivity
of similar crystals observed below 160 K. Two scenarios in which the $T^1$
scattering term is uniform or non-uniform around the Fermi surface are
discussed. As found previously by others, for uniform scattering the $T^1$
terms give scattering rates ($\tau^{-1}$) at lower $p$ that are somewhat larger
than the Planckian value $k_B T/\hbar$ and fall to zero for heavily OD
crystals. Near 160 K, $\tau^{-1}$ from the $T^2$ terms corresponds to the
Planckian value. | 2401.08380v1 |
2024-01-25 | Unveiling a Novel Metal-to-Metal Transition in LuH2: Critically Challenging Superconductivity Claims in Lutetium Hydrides | Following the recent report by Dasenbrock-Gammon et al. (2023) of
near-ambient superconductivity in nitrogen-doped lutetium trihydride
(LuH3-{\delta}N{\epsilon}), significant debate has emerged surrounding the
composition and interpretation of the observed sharp resistance drop. Here, we
meticulously revisit these claims through comprehensive characterization and
investigations. We definitively identify the reported material as lutetium
dihydride (LuH2), resolving the ambiguity surrounding its composition. Under
similar conditions (270-295 K and 1-2 GPa), we replicate the reported sharp
decrease in electrical resistance with a 30% success rate, aligning with
Dasenbrock-Gammon et al.'s observations. However, our extensive investigations
reveal this phenomenon to be a novel, pressure-induced metal-to-metal
transition intrinsic to LuH2, distinct from superconductivity. Intriguingly,
nitrogen doping exerts minimal impact on this transition. Our work not only
elucidates the fundamental properties of LuH2 and LuH3 but also critically
challenges the notion of superconductivity in these lutetium hydride systems.
These findings pave the way for future research on lutetium hydride systems
while emphasizing the crucial importance of rigorous verification in claims of
ambient temperature superconductivity. | 2401.13958v2 |
2024-02-06 | Homogeneity problem for basis expansion of functional data with applications to resistive memories | The homogeneity problem for testing if more than two different samples come
from the same population is considered for the case of functional data. The
methodological results are motivated by the study of homogeneity of electronic
devices fabricated by different materials and active layer thicknesses. In the
case of normality distribution of the stochastic processes associated with each
sample, this problem is known as Functional ANOVA problem and is reduced to
test the equality of the mean group functions (FANOVA). The problem is that the
current/voltage curves associated with Resistive Random Access Memories (RRAM)
are not generated by a Gaussian process so that a different approach is
necessary for testing homogeneity. To solve this problem two different
parametric and nonparametric approaches based on basis expansion of the sample
curves are proposed. The first consists of testing multivariate homogeneity
tests on a vector of basis coefficients of the sample curves. The second is
based on dimension reduction by using functional principal component analysis
of the sample curves (FPCA) and testing multivariate homogeneity on a vector of
principal components scores. Different approximation numerical techniques are
employed to adapt the experimental data for the statistical study. An extensive
simulation study is developed for analyzing the performance of both approaches
in the parametric and non-parametric cases. Finally, the proposed methodologies
are applied on three samples of experimental reset curves measured in three
different RRAM technologies. | 2402.04321v1 |
2024-02-17 | Fourier Electron Optics with Massless Dirac Fermions Scattered by Quantum Dot Lattice | The field of electron optics exploits the analogy between the movement of
electrons or charged quasiparticles, primarily in two-dimensional materials
subjected to electric and magnetic (EM) fields and the propagation of
electromagnetic waves in a dielectric medium with varied refractive index. We
significantly extend this analogy by introducing Fourier electron optics (FEO)
with massless Dirac fermions (MDF), namely the charge carriers of single-layer
graphene under ambient conditions, by considering their scattering from a
two-dimensional quantum dot lattice (TDQDL) treated within Lippmann-Schwinger
formalism. By considering the scattering of MDF from TDQDL with a cavity, as
well as the moir\'{e} pattern of twisted TDQDLs, we establish an electronic
analogue of Babinet's principle in optics. Exploiting the similarity of the
resulting differential scattering cross-section with the Fraunhofer diffraction
pattern, we construct a dictionary for such FEO. Subsequently, we evaluate the
resistivity of such scattered MDF using the Boltzmann approach as a function of
the angle made between the direction of propagation of these charge-carriers
and the symmetry axis of the dot-lattice, and Fourier analyze them to show that
the spatial frequency associated with the angle-resolved resistivity gets
filtered according to the structural changes in the dot lattice, indicating
wider applicability of FEO of MDF. | 2402.11259v1 |
2024-04-01 | Electronic structure and thermoelectric properties of epitaxial Sc1-xVxNy thin films grown on MgO(001) | The electronic structure of Sc1-xVxNy epitaxial films with different alloying
concentrations of V are investigated with respect to effects on thermoelectric
properties. Band structure calculations on Sc0.75V0.25N indicate that V 3d
states lie in the band gap of the parent ScN compound in the vicinity of the
Fermi level. Thus, theoretically the presence of light (dispersive) bands at
the {\Gamma}-point with band multiplicity is expected to lead to lower
electrical resistivity while flat (heavy) bands at X-W-K symmetry points are
associated with higher Seebeck coefficient than that of ScN. With this aim,
epitaxial Sc1-xVxNy thin film samples were deposited on MgO(001) substrates.
All the samples showed N substoichiometry and pseudocubic crystal structure.
The N-vacancy-induced states were visible in the Sc 2p XAS spectra. The
reference ScN and Sc1-xVxNy samples up to x = 0.12 were n type, exhibiting
carrier concentration of 1021 cm-3, typical for degenerate semiconductors. For
the highest V alloying of x = 0.15, holes became the majority charge carrier as
indicated by the positive Seebeck coefficient. The underlying electronic
structure and bonding mechanism in Sc1-xVxNy influence the electrical
resistivity, Seebeck coefficient, and Hall effect. Thus, the work contributes
to the fundamental understanding of the correlated defects and thermoelectric
properties to the electronic structure in Sc-N system with V alloying. | 2404.01417v1 |
2024-05-01 | Metamagnetism and anomalous magnetotransport properties in rare-earth-based polar semimetals $R$AuGe ($R =$ Dy, Ho, and Gd) | We report the magnetic, magnetoelastic, and magnetotransport properties of
single crystals of polar magnets $R$AuGe ($R=$ Dy, Ho, and Gd), grown by Au-Ge
self-flux. Magnetization and magnetostriction measurements reveal multi-step
metamagnetic transitions for the $c$-axis magnetic field ($H\parallel c$) for
DyAuGe and HoAuGe, suggesting magnetic frustration in the triangular lattice of
$R$ ions. The magnetic phase diagrams have clarified a close connection between
the magnetoelastic property and the emergence of the intermediate metamagentic
phase. The magnetic-field dependence of the resistivity and Hall resistivity
reveal the semimetallic transport dominated by hole-type carriers, consistent
with the behavior in a nonmagnetic analogue YAuGe. We also identify a signature
of an anomalous Hall effect (AHE) proportional to the field-induced
magnetization in $R=$ Dy, Ho, and Gd. GdAuGe shows magnetic and transport
behavior as reported in a previous study using Bi-flux grown single crystals,
while the self-flux grown crystal shows larger magnetoresistance ($\sim$ 345\%,
at 1.8 K and 9 T) due to higher hole-type carrier mobility ($\sim$ 6400
cm$^2$/Vs). Using the two-band model analysis considering the mobility change
during the magnetization process, we extract the anomalous Hall conductivity:
$\sim 1200$ S/cm and $\sim 530$ S/cm for $R=$ Dy and Ho, respectively, at 1.8 K
with 9 T for $H\parallel c$. The magnitude of conductivity suggests a
contribution of intrinsic origin, possibly related to the Berry curvature in
the electron bands induced by the time-reversal symmetry breaking and the polar
lattice. | 2405.00628v2 |
1995-10-03 | Theory of the Normal State of Cuprate Superconducting Materials | We have proposed a model Hamiltonian, which describes a simple physical
picture that the holes with single occupation constraint introduced by doping
move in the antiferromagnetic background of the copper spins, to describe the
normal state of the cuprate superconducting materials, and used the
renormalization group method to calculate its anomalous magnetic and transport
properties. The anomalous magnetic behavior of the normal state is controlled
by both the copper spin and the spin part of the doping hole residing on the O
sites. The physical resistivity is determined by both the
quasiparticle-spin-fluctuation and the quasiparticle-gauge-fluctuation
scatterings and the Hall coefficient is determined by the parity-odd gauge
interaction deriving from the nature of the hard-core boson which describes the
charge part of the doping holes. | 9510015v1 |
1999-03-04 | Transport in Materials with Disclination Dipoles: Applications to Polycrystals and Amorphous Dielectrics | The problem of both electron and phonon scattering by wedge disclination
dipoles (WDD) is studied in the framework of the deformation potential
approach. The exact analytical results for the mean free path are obtained
within the Born approximation. The WDD-induced contribution to the residual
resistivity in nanocrystalline metals is estimated. Using the WDD-based model
of a grain boundary, the thermal conductivity, kappa, of polycrystals and
amorphous dielectrics is studied. It is shown that the low-temperature
crossover of kappa experimentally observed in LiF, NaCl, and sapphire can be
explained by the grain-boundary phonon scattering. A combination of two
scattering processes, the phonon scattering due to biaxial WDD and the
Rayleigh-type scattering, is suggested to be of importance in amorphous
dielectrics. Our results are in a good agreement with the experimentally
observed kappa in a-SiO_2, a-GeO_2 a-Se, and polystyrene over a wide
temperature range. | 9903072v1 |
1999-05-06 | Role of Orbitals in Manganese Oxides - Ordering and Fluctuation | We study the manganese oxides from the viewpoint of the strongly correlated
doped Mott insulator. The magnetic ordering and the charge transport are
governed by the orbital degrees of freedom, and their dimensionality is
controlled by the anisotropic transfer integrals between the $e_g$ orbitals. As
x increases the magnetic structure is predicted to change as $A \to F \to A \to
C \to G$ (F: ferromagnet, A: layered antiferromagnet, C: rod-type
antiferromagnet, G: usual antiferromagnet), in agreement with experiments.
Especially the orbital is aligned as $d_{x^2-y^2}$ in the metallic A state,
which explains the quasi 2D transport and no canting of the spin observed
experimentally. Next we discuss the ferromagnetic state without the orbital
ordering due to the quantum fluctuation. Here the interplay between the
electron repulsion U and the Jahn-Teller electron-phonon interation $E_{LR}$ is
studied with a large d model. In addition to this strong correlation, we
propose that the dynamical phase separation could explain the specific heat as
well as the various anomalous physical properties, e.g., resistivity,
photo-emission, etc. | 9905072v1 |
1999-11-16 | Magneto-impedance of glass-coated Fe-Ni-Cu microwires | The magneto-impedance (MI) of glass-coated Fe-Ni-Cu microwires was
investigated for longitudinal radio-frequency (RF) currents up to a frequency
of 200 MHz using an RF lock-in amplifier method. The MI, defined as DZ/Z =
[Z(H)-Z(H=0.3T)]/Z(H=0.3T), displays a peak structure (negative MI) at zero
field for RF currents with frequencies less than 20MHz and this crosses over to
a sharp dip (positive MI) at higher frequencies. This crossover behavior is
ascribed to the skin-depth-limited response primarily governed by the
field-dependence of the permeability. Large saturation fields (300 to 600 Oe)
and other anomalies indicate the possible influence of giant magneto-resistance
(GMR) on the MI. | 9911241v1 |
2000-11-18 | Magneto-electronic Properties of a Ferrimagnetic Semiconductor: The Hybrid Cupromanganite CaCu3Mn4O12 | The mixed manganite-cuprate CaCu3Mn4O12 is found, using density functional
methods, to be a narrow gap (90 meV calculated) ferrimagnetic semiconductor. Cu
(formally S=1/2) antialigns with Mn (formally S=3/2), and the net spin moment
is 9 \mu_B consistent with the formal spins. Holes have Cu d_{xy}-O p_{\sigma}
(i.e. antibonding dp\sigma) character with spins aligned antiparallel to the
net magnetization; electrons have the opposite spin and have mixed Cu d_{xy} -
Mn e_g character. Thermally excited electrons and holes will each be fully spin
polarized, but in opposite directions. The properties of this material are
strongly tied to the distorted quadruple perovskite structure, which is closely
related to the skutterudite structure. The observed resistivity,
magnetoresistance, and magnetization are discussed in terms of our results. | 0011316v1 |
2001-06-15 | Pressure-induced recovery of the Fermi-liquid state in the non-Fermi liquid material U2Pt2In | In the study of non-Fermi-liquid (NFL) phenomena in correlated metals,
U2Pt2In is of special interest as it is one of the rare stoichiometric
(undoped) materials that show NFL behaviour at ambient pressure. Here we report
on the stability of the NFL phase with respect to hydrostatic pressure (p< 1.8
GPa). Electrical resistivity data under pressure, taken on a single-crystalline
sample for a current in the tetragonal plane, show that T_FL, i.e. the
temperature below which the Fermi-liquid T^2-term is observed, increases with
pressure as T_FL ~ (p-p_c), where p_c~0 is a critical pressure. This provides
strong evidence for the location of U2Pt2In at an antiferromagnetic quantum
critical point. | 0106292v1 |
2002-04-25 | Interpretation of large room-temperature diamagnetism at low magnetic fields in films of oxidised atactic polypropylene in terms of superconducting current loops | A simple model is used to analyse published results on large room-temperature
diamagnetism for two films of oxidised atactic polypropylene (OAPP) at low
magnetic fields. The model involves induced currents expected in circular
closed loops of superconductors in fields below the lower critical field H_{c1}
at which flux penetration would first occur if a metamagnetic transition did
not intervene as in OAPP, and the assumption that resistance would be restored
at H_{c1} (negligible pinning). Fits to the data for the more strongly magnetic
sample with the model, allowing two different types of loops with different
loop radii b_1 and b_2, but with the same cross section a of loop material
yield H_{c1} is approximately equal to 5260 Oe, and fits to the data for the
less strongly magnetic sample with two loop sizes and with the same value of
H_{c1}, combined with the knowledge that the minimum number of closed loops of
any type is one, requires that the radius a of the cross section of the
material should be less than about 0.8 micrometres, in fair agreement with a
maximum radius of 1 micrometre obtained previously from other data. | 0204556v1 |
2002-08-28 | Low frequency 1/f noise in doped manganite grain-boundary junctions | We have performed a systematic analysis of the low frequency 1/f-noise in
single grain boundary junctions in the colossal magnetoresistance material
La_{2/3}Ca_{1/3}MnO_{3-delta}. The grain boundary junctions were formed in
epitaxial La_{2/3}Ca_{1/3}MnO_{3-delta} films deposited on SrTiO_3 bicrystal
substrates and show a large tunneling magnetoresistance of up to 300% at 4.2 K
as well as ideal, rectangular shaped resistance versus applied magnetic field
curves. Below the Curie temperature T_C the measured 1/f noise is dominated by
the grain boundary. The dependence of the noise on bias current, temperature
and applied magnetic field gives clear evidence that the large amount of low
frequency noise is caused by localized sites with fluctuating magnetic moments
in a heavily disordered grain boundary region. At 4.2 K additional temporally
unstable Lorentzian components show up in the noise spectra that are most
likely caused by fluctuating clusters of interacting magnetic moments. Noise
due to fluctuating domains in the junction electrodes is found to play no
significant role. | 0208556v1 |
2002-11-14 | Variable-Range Hopping of Spin Polarons: Magnetoresistance in a Modified Mott Regime | We analize electrical conductivity controlled by hopping of bound spin
polarons in disordered solids with wide distributions of electron energies and
polaron shifts (barriers). By means of percolation theory and Monte Carlo
simulations we have shown that in such materials at low temperatures, when
hopping occurs in the vicinity of the Fermi level, a hard polaron gap does not
manifest itself in the transport properties. This happens because as
temperature decreases the hopping polaron trades the decreasing electron and
polaron barriers for increasing hopping distance. As a result, in the absence
of the Coulomb correlation effects, in this variable-range variable-barrier
hopping regime, the electrical resistivity as a function of temperature obeys a
non-activation law, which differs from the standard Mott law. | 0211301v1 |
2002-11-15 | Ultra-sharp magnetization steps in perovskite manganites | We report a detailed study of step-like metamagnetic transitions in the
magnetization and resistivity of polycrystalline Pr0.5Ca0.5Mn0.95Co0.05O3. The
steps have a sudden onset below a critical temperature, are extremely sharp
(width < 0.2 mT), and occur at critical fields which are linearly dependent on
the absolute value of the cooling field in which the sample is prepared.
Similar transitions are also observed at low temperature in non-Co doped
manganites, including single crystal samples. These data show that the steps
are an intrinsic property, qualitatively different from either previously
observed higher temperature metamagnetic transitions in the manganites or
metamagnetic transitions observed in other materials. | 0211337v1 |
2003-04-02 | Low Friction Flows of Liquids at Nanopatterned Interfaces | With the recent important development of microfluidic systems,
miniaturization of flow devices has become a real challenge. Microchannels,
however, are characterized by a large surface to volume ratio, so that surface
properties strongly affect flow resistance in submicrometric devices. We
present here results showing that the concerted effect of wetting . properties
and surface roughness may considerably reduce friction of the fluid past the
boundaries. The slippage of the fluid at the channel boundaries is shown to be
drastically increased by using surfaces that are patterned at the nanometer
scale. This effect occurs in the regime where the surface pattern is partially
dewetted, in the spirit of the 'superhydrophobic' effects that have been
recently discovered at the macroscopic scales. Our results show for the first
time that, in contrast to the common belief, surface friction may be reduced by
surface roughness. They also open the possibility of a controlled realization
of the 'nanobubbles' that have long been suspected to play a role in
interfacial slippage | 0304037v1 |
2003-05-30 | A Low-Temperature Atomic Layer Deposition Liftoff Method for Microelectronic and Nanoelectronic Applications | We report a novel method for depositing patterned dielectric layers with
sub-micron features using atomic layer deposition (ALD). The patterned films
are superior to sputtered or evaporated films in continuity, smoothness,
conformality, and minimum feature size. Films were deposited at 100-150C using
several different precursors and patterned using either PMMA or photoresist.
The low deposition temperature permits uniform film growth without significant
outgassing or hardbaking of resist layers. A liftoff technique presented here
gives sharp step edges with edge roughness as low as ~10 nm. We also measure
dielectric constants (k) and breakdown fields for the high-k materials aluminum
oxide (k ~ 8-9), hafnium oxide (k ~ 16-19) and zirconium oxide (k ~ 20-29),
grown under similar low temperature conditions. | 0305711v2 |
2003-11-13 | Structural, magnetic and transport properties of thin films of the Heusler alloy Co2MnSi | Thin films of Co2MnSi have been grown on a-plane sapphire substrates from
three elemental targets by dc magnetron co-sputtering. These films are single
phase, have a strong (110) texture and a saturation magnetization of 4.95
uB/formula unit at 10 K. Films grown at the highest substrate temperature of
715 K showed the lowest resistivity (47 uOhm cm at 4.2 K) and the lowest
coercivity (18 Oe). The spin polarization of the transport current was found to
be of the order of 54% as determined by point contact Andreev reflection
spectroscopy. A decrease in saturation magnetization with decreasing film
thickness and different transport behaviour in thinner films indicate a graded
disorder in these films grown on non-lattice matched substrates. | 0311316v1 |
2004-05-17 | Itinerant Ferromagnetism and Superconductivity | Superconductivity has again become a challenge following the discovery of
unconventional superconductivity. Resistance-free currents have been observed
in heavy-fermion materials, organic conductors and copper oxides. The discovery
of superconductivity in a single crystal of $UGe_2$, $ZrZn_2$ and $URhGe$
revived the interest in the coexistence of superconductivity and
ferromagnetism. The experiments indicate that: i)The superconductivity is
confined to the ferromagnetic phase. ii)The ferromagnetic order is stable
within the superconducting phase (neutron scattering experiments). iii) The
specific heat anomaly associated with the superconductivity in these materials
appears to be absent. The specific heat depends on the temperature linearly at
low temperature.
I present a review of the recent experimental results and the basic
theoretical ideas concerning ferromagnetic superconductivity
(FM-superconductivity) induced by the ferromagnetic spin fluctuations. A
particular attention is paid to the magnon exchange mechanism of
FM-superconductivity. | 0405371v2 |
2005-01-08 | Silver paint as a soldering agent for DyBaCuO single-domains welding | Silver paint has been tested as a soldering agent for DyBaCuO single-domain
welding. Junctions have been manufactured on Dy-Ba-Cu-O single-domains cut
either along planes parallel to the c-axis or along the ab-planes.
Microstructural and superconducting characterisations of the samples have been
performed. For both types of junctions, the microstructure in the joined area
is very clean: no secondary phase or Ag particles segregation has been
observed. Electrical and magnetic measurements for all configurations of
interest are reported $\rho(T)$ curves, and Hall probe mapping). The narrow
resistive superconducting transition reported for all configurations shows that
the artificial junction does not affect significantly the measured
superconducting properties of the material. | 0501163v1 |
2005-01-19 | Magnetism and Transport in YbMn2Sb2 | A new ternary intermetallic compound, namely, YbMn2Sb2, has been synthesized
and its magnetic and electrical transport properties have been studied in the
temperature range of 2 to 300 K. This compound crystallizes in a trigonal,
La2O2S type structure (space group P3bm1, No. 164) and is found to be
ferromagnetically ordered at room temperature. The magnetism is attributed to
the ordering of Mn sublattice. M5 xray absorption spectrum of YbMn2Sb2 obtained
at room temperature suggests that the valency of Yb in this compound is close
to 2. Electrical resistivity of this compound is metal like and a positive
magnetoresistance of 13 percent is observed at 5 K in an applied field of 9T.
Key words Rare earth intermetallics and alloys, Magnetic properties, Xray
absorption spectroscopy, Electrical transport. | 0501450v1 |
2005-03-08 | Ultra low threshold current THz quantum cascade lasers based on buried strip-waveguides | THz quantum cascade lasers based on a novel buried cavity geometry are
demonstrated by combining double-metal waveguides with proton implantation.
Devices are realised with emission at 2.8 THz, displaying ultra low threshold
currents of 19 mA at 4K in both pulsed and continuous wave operation. Thanks to
the semiconductor material on both sides of the active region and to the narrow
width of the top metal strip, the thermal properties of these devices have been
greatly improved. A decrease of the thermal resistance by over a factor of two
compared to standard ridge double-metal lasers of similar size has been
measured. | 0503186v1 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.