publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
|---|---|---|---|
2010-07-01 | First tests of "bulk" MICROMEGAS with resistive cathode mesh | We present the first results from tests of a MICROMEGAS detector manufactured
using the so-called "bulk" technology and having a resistive cathode mesh
instead of the conventional metallic one. This detector operates as usual
MICROMEGAS, but in the case of sparks, which may appear at high gas gains, the
resistive mesh reduces their current and makes the sparks harmless. This
approach could be complementary to the ongoing efforts of various groups to
develop spark-protected MICROMEGAS with resistive anode planes. | 1007.0211v1 |
2010-07-08 | Microwave zero-resistance states in a bilayer electron system | Magnetotransport measurements on a high-mobility electron bilayer system
formed in a wide GaAs quantum well reveal vanishing dissipative resistance
under continuous microwave irradiation. Profound zero-resistance states (ZRS)
appear even in the presence of additional intersubband scattering of electrons.
We study the dependence of photoresistance on frequency, microwave power. and
temperature. Experimental results are compared with a theory demonstrating that
the conditions for absolute negative resistivity correlate with the appearance
of ZRS. | 1007.1393v1 |
2011-05-17 | Microwave-induced Hall resistance in bilayer electron systems | The influence of microwave irradiation on dissipative and Hall resistance in
high-quality bilayer electron systems is investigated experimentally. We
observe a deviation from odd symmetry under magnetic field reversal in the
microwave-induced Hall resistance $\Delta R_{xy}$ whereas the dissipative
resistance $\Delta R_{xx}$ obeys even symmetry. Studies of $\Delta R_{xy}$ as a
function of the microwave electric field and polarization exhibit a strong and
non-trivial power and polarization dependence. The obtained results are
discussed in connection to existing theoretical models of microwave-induced
photoconductivity. | 1105.3362v1 |
2011-12-02 | Mooij Rule and Weak Localization | It has been shown that the observed correlation between the resistivity
$\rho$ of high-resistive metallic alloys and the sign of the temperature
derivative $d\rho/dT$ can be explained by taking into account the weak
localization. This correlation is known as Mooij rule: the derivative
$d\rho/dT$ is negative for alloys with resistivity in the range of
$300\div150\,\mu\Omega\cdot$cm, which corresponds to the electron mean free
path about the interatomic distance; however, this derivative is positive for
alloys with lower resistivity. | 1112.0429v1 |
2015-03-16 | High pressure investigation of superconducting signatures in CeCu$_{2}$Si$_{2}$ : ac- magnetic susceptibility and heat capacity, resistivity and thermopower | Taking advantage of a novel multiprobe setup we have measured, on a unique
sample, the ac-magnetic susceptibility, the resistivity, the ac-specific heat
and the thermopower of the superconductor heavy fermion CeCu$_{2}$Si$_{2}$
under pressure up to 5.1 GPa. At the superconducting transition temperature
$T_c$, the Meissner signal corresponds to that expected for the sample volume
and coincides with the specific heat jump and the resistive transition
completion temperatures. Differing from previous observations, here the
susceptibility measurements did not reveal any anomaly in the vicinity of the
resistive transition onset. | 1503.04861v2 |
2024-05-14 | Experimental Demonstration of Turbulence-resistant Lidar via Quantum Entanglement | We report a proof-of-principle experimental demonstration of a
turbulence-resistant quantum Lidar system. As a key technology for sensing and
ranging, Lidar has drawn considerable attention for a study from quantum
perspective, in search of proven advantages complementary to the capabilities
of conventional Lidar technologies. Environmental factors such as strong
atmospheric turbulence can have detrimental effects on the performance of these
systems. We demonstrate the possibility of turbulence-resistant operation of a
quantum Lidar system via two-photon interference of entangled photon pairs.
Additionally, the reported quantum Lidar also demonstrates the expected noise
resistance. This study suggests a potential high precision timing-positioning
technology operable under turbulence and noise. | 2405.08916v1 |
2020-11-26 | Systematic study of nonmagnetic resistance changes due to electrical pulsing in single metal layers and metal/antiferromagnet bilayers | Intense current pulses are often required to operate microelectronic and
spintronic devices. Notably, strong current pulses have been shown to induce
magnetoresistance changes attributed to domain reorientation in
antiferromagnet/heavy metal bilayers and non-centrosymmetric antiferromagnets.
In such cases, nonmagnetic resistivity changes may dominate over signatures of
antiferromagnetic switching. We report systematic measurements of the
current-induced changes of the transverse and longitudinal resistance of Pt and
Pt/NiO layers deposited on insulating substrates, namely Si/SiO$_2$,
Si/Si$_3$N$_4$, and Al$_2$O$_3$. We identify the range of pulse amplitude and
length that can be used without affecting the resistance and show that it
increases with the device size and thermal diffusivity of the substrate. No
significant difference is observed in the resistive response of Pt and NiO/Pt
devices, thus precluding evidence on the switching of antiferromagnetic domains
in NiO. The variation of the transverse resistance is associated to a
thermally-activated process in Pt that decays following a double exponential
law with characteristic timescales of a few minutes to hours. We use a
Wheatstone bridge model to discriminate between positive and negative
resistance changes, highlighting competing annealing and electromigration
effects. Depending on the training of the devices, the transverse resistance
can either increase or decrease between current pulses. Further, we elucidate
the origin of the nonmonotonic resistance baseline, which we attribute to
training effects combined with the asymmetric distribution of the current.
These results provide insight into the origin of current-induced resistance
changes in metal layers and a guide to minimize nonmagnetic artifacts in
switching experiments of antiferromagnets. | 2011.13413v1 |
2013-04-17 | Universal density scaling of disorder-limited low-temperature conductivity in high-mobility two-dimensional systems | We theoretically consider the carrier density dependence of low-temperature
electrical conductivity in high-quality and low-disorder two-dimensional (2D)
`metallic' electronic systems such as 2D GaAs electron or hole quantum wells or
gated graphene. Taking into account resistive scattering by Coulomb disorder
arising from quenched random charged impurities in the environment, we show
that the 2D conductivity \sigma(n) varies as \sigma ~ n^{\beta(n)} as a
function of the 2D carrier density n where the exponent \beta(n) is a smooth,
but non-monotonic, function of density with possible nontrivial extrema. In
particular, the density scaling exponent \beta(n) depends qualitatively on
whether the Coulomb disorder arises primarily from remote or background charged
impurities or short-range disorder, and can, in principle, be used to
characterize the nature of the dominant background disorder. A specific
important prediction of the theory is that for resistive scattering by remote
charged impurities, the exponent \beta can reach a value as large as 2.7 for
k_F d ~ 1, where k_F ~\sqrt{n} is the 2D Fermi wave vector and d is the
separation of the remote impurities from the 2D layer. Such an exponent \beta
(>5/2) is surprising because unscreened Coulomb scattering by remote impurities
gives a limiting theoretical scaling exponent of \beta = 5/2, and naively one
would expect \beta(n) \le 5/2 for all densities since unscreened Coulomb
scattering should nominally be the situation bounding the resistive scattering
from above. We find numerically and show theoretically that the maximum value
of \alpha (\beta), the mobility (conductivity) exponent, for 2D semiconductor
quantum wells is around 1.7 (2.7) for all values of d (and for both electrons
and holes) with the maximum \alpha occurring around k_F d ~ 1. We discuss
experimental scenarios for the verification of our theory. | 1304.4668v1 |
2014-03-16 | Comparison of Sn-doped and nonstoichiometric vertical-Bridgman-grown crystals of the topological insulator Bi2Te2Se | A comparative study of the properties of topological insulator Bi2Te2Se (BTS)
crystals grown by the vertical Bridgeman method is described. Two defect
mechanisms that create acceptor impurities to compensate for the native n-type
carriers are compared: Bi excess, and light Sn doping. Both methods yield low
carrier concentrations and an n-p crossover over the length of the grown
crystal boules, but lower carrier concentrations and higher resistivities are
obtained for the Sn-doped crystals, which reach carrier concentrations as low
as 8 x 1014 cm-3. Further, the temperature dependent resistivities for the
Sn-doped crystals display strongly activated behavior at high temperatures,
with a characteristic energy of half the bulk band gap. The (001) cleaved
Sn-doped BTS crystals display high quality Shubnikov de Haas (SdH) quantum
oscillations due to the topological surface state electrons. Angle resolved
photoelectron spectroscopy (ARPES) characterization shows that the Fermi energy
(EF) for the Sn-doped crystals falls cleanly in the surface states with no
interference from the bulk bands, that the Dirac point for the surface states
lies approximately 60 meV below the top of the bulk valence band maximum, and
allows for a determination of the bulk and surface state carrier concentrations
as a function of Energy near EF. Electronic structure calculations that compare
Bi excess and Sn dopants in BTS demonstrate that Sn acts as a special impurity,
with a localized impurity band that acts as a charge buffer occurring inside
the bulk band gap. We propose that the special resonant level character of Sn
in BTS gives rise to the exceptionally low carrier concentrations and activated
resistivities observed. | 1403.3870v1 |
2015-02-13 | Epitaxial graphene on SiC: Modification of structural and electron transport properties by substrate pretreatment | The electrical transport properties of epitaxial graphene layers are
correlated with the SiC surface morphology. In this study we show by atomic
force microscopy and Raman measurements that the surface morphology and the
structure of the epitaxial graphene layers change significantly when different
pretreatment procedures are applied to nearly on-axis 6H-SiC(0001) substrates.
It turns out that the often used hydrogen etching of the substrate is
responsible for undesirable high macro steps evolving during graphene growth. A
more advantageous type of sub-nanometer stepped graphene layers is obtained
with a new method: a high-temperature conditioning of the SiC surface in argon
atmosphere. The results can be explained by the observed graphene buffer layer
domains after the conditioning process which suppress giant step bunching and
graphene step flow growth. The superior electronic quality is demonstrated by a
less extrinsic resistance anisotropy obtained in nano-probe transport
experiments and by the excellent quantization of the Hall resistance in
low-temperature magneto-transport measurements. The quantum Hall resistance
agrees with the nominal value (half of the von Klitzing constant) within a
standard deviation of 4.5*10(-9) which qualifies this method for the
fabrication of electrical quantum standards. | 1502.03927v3 |
2020-07-09 | Growth, Properties, and Applications of Pulsed Laser Deposited Nanolaminate Ti3AlC2 Thin Films | Recently, nanolaminated ternary carbides have attracted immense interest due
to the concomitant presence of both ceramic and metallic properties. Here, we
grow nanolaminate Ti3AlC2 thin films by pulsed laser deposition on
c-axis-oriented sapphire substrates and, surprisingly, the films are found to
be highly oriented along the (103) axis normal to the film plane, rather than
the (000l) orientation. Multiple characterization techniques are employed to
explore the structural and chemical quality of these films, the electrical and
optical properties, and the device functionalities. The 80-nm thick Ti3AlC2
film is highly conducting at room temperature (resistivity of 50 micro ohm-cm),
and a very-low-temperature coefficient of resistivity. The ultrathin (2 nm)
Ti3AlC2 film has fairly good optical transparency and high conductivity at room
temperature (sheet resistance of 735 ohm). Scanning tunneling microscopy
reveals the metallic characteristics (with finite density of states at the
Fermi level) at room temperature. The metal-semiconductor junction of the
p-type Ti3AlC2 film and n-Si show the expected rectification (diode)
characteristics, in contrast to the ohmic contact behavior in the case of
Ti3AlC2 on p-Si. A triboelectric-nanogenerator-based touch-sensing device,
comprising of the Ti3AlC2 film, shows a very impressive peak-to-peak
open-circuit output voltage of 80 V. These observations reveal that pulsed
laser deposited Ti3AlC2 thin films have excellent potential for applications in
multiple domains, such as bottom electrodes, resistors for high-precision
measurements, Schottky diodes, ohmic contacts, fairly transparent ultrathin
conductors, and next-generation biomechanical touch sensors for energy
harvesting. | 2007.04798v1 |
2022-01-19 | Tearing instability and current-sheet disruption in the turbulent dynamo | Turbulence in a conducting plasma can amplify seed magnetic fields in what is
known as the turbulent, or small-scale, dynamo. The associated growth rate and
emergent magnetic-field geometry depend sensitively on the material properties
of the plasma, in particular on the Reynolds number ${\rm Re}$, the magnetic
Reynolds number ${\rm Rm}$, and their ratio ${\rm Pm}\equiv{\rm Rm}/{\rm Re}$.
For ${\rm Pm} > 1$, the amplified magnetic field is gradually arranged into a
folded structure, with direction reversals at the resistive scale and field
lines curved at the larger scale of the flow. As the mean magnetic energy grows
to come into approximate equipartition with the fluid motions, this folded
structure is thought to persist. Using analytical theory and high-resolution
MHD simulations with the Athena++ code, we show that these magnetic folds
become unstable to tearing during the nonlinear stage of the dynamo for ${\rm
Rm}\gtrsim 10^4$ and ${\rm Re}\gtrsim 10^3$. An ${\rm Rm}$- and ${\rm
Pm}$-dependent tearing scale, at and below which folds are disrupted, is
predicted theoretically and found to match well the characteristic
field-reversal scale measured in the simulations. The disruption of folds by
tearing increases the ratio of viscous-to-resistive dissipation. In the
saturated state, the magnetic-energy spectrum exhibits a sub-tearing-scale
steepening to a slope consistent with that predicted for tearing-mediated
Alfv\'enic turbulence. Its spectral peak appears to be independent of the
resistive scale and comparable to the driving scale of the flow, while the
magnetic energy resides in a broad range of scales extending down to the
field-reversal scale set by tearing. Emergence of a degree of large-scale
magnetic coherence in the saturated state of the turbulent dynamo may be
consistent with observations of magnetic-field fluctuations in galaxy clusters
and recent laboratory experiments. | 2201.07757v2 |
2014-04-10 | Metal-insulator transition upon heating and negative-differential-resistive-switching induced by self-heating in BaCo0.9Ni0.1S1.8 | The layered compound BaCo1-xNixS2-y (0.05<x<0.2 and 0.05<y<0.2) exhibits an
unusual first-order structural and electronic phase transition from a low-T
monoclinic paramagnetic metal to a high-T tetragonal antiferromagnetic
insulator around 200 K with huge hysteresis (~ 40 K) and large volume change
(~0.01). Here we report on unusual voltage-controlled resistive switching
followed by current-controlled resistive switching induced by self-heating in
polycrystalline BaCo1-xNixS2-y (nominal x=0.1 and y=0.2). These were due to the
steep metal to insulator transition upon heating followed by the activated
behavior of the resistivity above the transition. The major role of Joule
heating in switching is supported by the absence of nonlinearity in the current
as function of voltage, I(V), obtained in pulsed measurements, in the range of
electric fields relevant to d.c. measurements. The voltage-controlled negative
differential resistance around the threshold for switching was explained by a
simple model of self-heating. The main difficulty in modeling I(V) from the
samples resistance as function of temperature R(T) was the progressive increase
of R(T), and to a lesser extend the decrease of the resistance jumps at the
transitions, caused by the damage induced by cycling through the transitions by
heating or self-heating. This was dealt with by following systematically R(T)
over many cycles and by using the data of R(T) in the heating cycle closest to
that of the self-heating one. | 1404.2773v1 |
2014-07-17 | Robust recipe for low-resistance ohmic contacts to a two-dimensional electron gas in a GaAs/AlGaAs heterostructure | The study of electron transport in low-dimensional systems is of importance,
not only from a fundamental point of view, but also for future electronic and
spintronic devices. In this context heterostructures containing a
two-dimensional electron gas (2DEG) are a key technology. In particular
GaAs/AlGaAs heterostructures, with a 2DEG at typically 100 nm below the
surface, are widely studied. In order to explore electron transport in such
systems, low-resistance ohmic contacts are required that connect the 2DEG to
macroscopic measurement leads at the surface. Here we report on designing and
measuring a dedicated device for unraveling the various resistance
contributions in such contacts, which include pristine 2DEG series resistance,
the 2DEG resistance under a contact, the contact resistance itself, and the
influence of pressing a bonding wire onto a contact. We also report here a
robust recipe for contacts with very low resistance, with values that do not
change significantly for annealing times between 20 and 350 sec, hence
providing the flexibility to use this method for materials with different 2DEG
depths. The type of heating used for annealing is found to strongly influence
the annealing process and hence the quality of the resulting contacts. | 1407.4781v1 |
2017-03-10 | Contact resistance at planar metal contacts on bilayer graphene and effects of molecular insertion layers | The possible origins of metal-bilayer graphene (BLG) contact resistance are
investigated by taking into consideration the bandgap formed by interfacial
charge transfer at the metal contacts. Our results show that a charge injection
barrier (Schottky barrier) does not contribute to the contact resistance
because the BLG under the contacts is always degenerately doped. We also showed
that the contact-doping-induced increase in the density of states (DOS) of BLG
under the metal contacts decreases the contact resistance owing to enhanced
charge carrier tunnelling at the contacts. The contact doping can be enhanced
by inserting molecular dopant layers into the metal contacts. However, carrier
tunnelling through the insertion layer increases the contact resistance, and
thus, alternative device structures should be employed. Finally, we showed that
the inter-band transport by variable range hopping via in-gap states is the
largest contributor to contact resistance when the carrier type of the gated
channel is opposite to the contact doping carrier type. This indicates that the
strategy of contact resistance reduction by the contact-doping-induced increase
in the DOS is effective only for a single channel transport branch (n- or
p-type) depending on the contact doping carrier type. | 1703.03521v1 |
2018-12-04 | On the extraction of resistivity and area of nanoscale interconnect lines by temperature-dependent resistance measurements | Several issues concerning the applicability of the temperature coefficient of
the resistivity (TCR) method to scaled interconnect lines are discussed. The
central approximation of the TCR method, the substitution of the interconnect
wire TCR by the bulk TCR becomes doubtful when the resistivity of the conductor
metal is strongly increased by finite size effects. Semiclassical calculations
for thin films show that the TCR deviates from bulk values when the surface
roughness scattering contribution to the total resistivity becomes significant
with respect to grain boundary scattering, an effect that might become even
more important in nanowires due to their larger surface-to-volume ration. In
addition, the TCR method is redeveloped to account for line width roughness. It
is shown that for rough wires, the TCR method yields the harmonic average of
the cross-sectional area as well as, to first order, the accurate value of the
resistivity at the extracted area. Finally, the effect of a conductive barrier
or liner layer on the TCR method is discussed. It is shown that the liner or
barrier parallel conductance can only be neglected when it is lower than about
5 to 10% of the total conductance. It is furthermore shown that neglecting the
liner/barrier parallel conductance leads mainly to an overestimation of the
cross-sectional area of the center conductor whereas its resistivity is less
affected. | 1812.01379v1 |
2021-12-21 | On the origin and the amplitude of T-square resistivity in Fermi liquids | In 1937, Baber, Landau and Pomeranchuk postulated that collisions between
electrons generates a contribution to the electric resistivity of metals with a
distinct T$^2$ temperature dependence. The amplitude of this term is small in
common metals, but dominant in metals hosting either heavy carriers or a low
concentration of them. The link between the temperature dependence and the size
of the scattering phase space is straightforward, but not the microscopic
source of dissipation. To explain how electron-electron collisions lead to
momentum leak, Umklapp events or multiple electron reservoirs have been
invoked. This interpretation is challenged by a number of experimental
observations: the persistence of T-square resistivity in dilute metals (in
which the two mechanisms are irrelevant), the successful extension of
Kadowaki-Woods scaling to dilute metals, and the observation of a
size-dependent T-square thermal resistivity ($T/\kappa$) and its
Wiedemann-Franz (WF) correlation with T-square electrical resistivity. This
paper argues that much insight is provided by the case of normal liquid $^3$He
where the T-square temperature dependence of energy and momentum diffusivity is
driven by fermion-fermion collisions. The amplitude of T-square resistivity in
$^3$He and in metals share a common scaling. Thus, the ubiquitous T-square
electrical resistivity ultimately stems from the Fermi-liquid temperature
dependence of momentum diffusivity. | 2112.11092v3 |
2022-03-30 | One Dimensional Wormhole Corrosion in Metals | Corrosion is a ubiquitous failure mode of materials in extreme environments.
The more localized it is, the more difficult it is to detect and more
deleterious its effects. Often, the progression of localized corrosion is
accompanied by the evolution of porosity in materials, creating internal
void-structures that facilitate the ingress of the external environment into
the interior of the material, further accelerating the internal corrosion.
Previously, the dominant morphology of such void-structures has been reported
to be either three-dimensional (3D) or two-dimensional (2D). Here, we report a
more localized form of corrosion, which we call 1D wormhole corrosion. Using
electron tomography, we show multiple examples of this 1D and percolating
morphology that manifests a significantly high aspect ratio differentiable from
2D and 3D corrosion. To understand the origin of this mechanism in a Ni-Cr
alloy corroded by molten salt, we combined energy-filtered four-dimensional
scanning transmission electron microscopy (EF-4D-STEM) and ab initio density
functional theory (DFT) calculations to develop a vacancy mapping method with
nanometer-resolution, identifying a remarkably high vacancy concentration in
the diffusion-induced grain boundary migration (DIGM) zone, up to 100 times the
equilibrium value at the melting point. These vacancy supersaturation regions
act as the precursors of wormholes, and lead to the asymmetrical growth of
voids along GBs. We show that similar 1D penetrating corrosion morphologies
could also occur in other materials or corrosion conditions, implying the broad
impact of this extremely localized corrosion mechanism. Deciphering the origins
of 1D corrosion is an important step towards designing structural materials
with enhanced corrosion resistance, and also offers new pathways to create
ordered-porous materials for functional applications. | 2203.16312v1 |
2018-06-28 | Thermomechanical response of thickly tamped targets and diamond anvil cells under pulsed hard x-ray irradiation | In the laboratory study of extreme conditions of temperature and density, the
exposure of matter to high intensity radiation sources has been of central
importance. Here we interrogate the performance of multi-layered targets in
experiments involving high intensity, hard x-ray irradiation, motivated by the
advent of extremely high brightness hard x-ray sources, such as free electron
lasers and 4th-generation synchrotron facilities. Intense hard x-ray beams can
deliver significant energy in targets having thick x-ray transparent layers
(tampers) around samples of interest, for the study of novel states of matter
and materials' dynamics. Heated-state lifetimes in such targets can approach
the microsecond level, regardless of radiation pulse duration, enabling the
exploration of conditions of local thermal and thermodynamic equilibrium at
extreme temperature in solid density matter. The thermal and mechanical
response of such thick layered targets following x-ray heating, including
hydrodynamic relaxation and heat flow on picosecond to millisecond timescales,
is modelled using radiation hydrocode simulation, finite element analysis, and
thermodynamic calculations. Assessing the potential for target survival over
one or more exposures, and resistance to damage arising from heating and
resulting mechanical stresses, this study doubles as an investigation into the
performance of diamond-anvil high pressure cells under high x-ray fluences.
Long used in conjunction with synchrotron x-ray radiation and high power
optical lasers, the strong confinement afforded by such cells suggests novel
applications at emerging high intensity x-ray facilities and new routes to
studying thermodynamic equilibrium states of warm, very dense matter. | 1806.10893v2 |
2021-01-13 | Fermi Level Engineering and Mechanical Properties of High Entropy Carbides | Fermi level engineering and mechanical properties evolution in high entropy
carbides are investigated by theoretical and experimental means. Massive
elemental diversity in high entropy ceramics broadens the compositional space
but imposes great challenges in composition selection and property
investigation. We have utilized the valence electron concentration (VEC)
descriptor to design and predict properties of high entropy carbides. The VEC
regulates the Fermi energy and systematically alters the bonding
characteristics of materials. As a result, mechanical properties evolve as
function of the VEC. At VEC 8.4, the strong {\sigma} bonding states stem from
filled overlapping metal d and carbon p orbitals, which results in maximum
resistance to shear deformation and highest hardness. Beyond or below the
optimum VEC point of 8.4, mechanical response degrades due to filling or
emptying of energy orbitals that facilitates shear deformation. Furthermore,
the optimum VEC point can shift based on the constituent metals that formulate
the high entropy carbide. Our analyses demonstrate strong correlation between
calculated hardness and shear modulus. As an experimental complement, a set of
high entropy carbides are synthesized, and mechanical properties investigated.
The measured hardness follows theoretical predictions and the highest hardness
of ~30 GPa is achieved at VEC 8.4. In contrast, hardness decreases by 50% when
VEC is 9.4. Designing high entropy carbides based on VEC and understanding
mechanical properties at an electronic level enables one to manipulate the
composition spectrum to procure a desired mechanical response from a chemically
disordered crystal. | 2101.04885v1 |
2022-12-01 | Magnetic and Electrical Properties of high-entropy rare-earth manganites | Detailed investigations of structural, magnetic and electronic transport
properties of hole-doped high-entropy rare-earth manganites are presented. The
high-entropy samples (LaNdPrSmEu)$_{1-x}$Sr$_x$MnO$_3$
(0$\leq$\textit{x}$\leq$0.5), synthesized using the solid-state technique, show
a change in the crystal structure from \textit{Pbnm} to \textit{R-3c} with
increasing Sr substitution, attributed to the change in the tolerance factor.
Prominent ferromagnetic ordering is observed in the sample with a rhombohedral
structure (\textit{x}$\geq$0.3), originating from the dominant double exchange
mechanism mediated by itinerant electrons. Further, the Curie temperature is
smaller for the high-entropy sample with \textit{x}=0.3, as compared to
La$_{0.7}$Sr$_{0.3}$MnO$_3$, suggesting a strong relation between the Curie
temperature and the Mn-O-Mn bond angle associated with the reduced ionic radii
at the rare-earth site. The electrical resistivity of the high-entropy samples
is larger than those of La$_{1-x}$Sr$_x$MnO$_3$, which can be ascribed to the
reduced bandwidth due to the enhanced structural distortion. A concomitant rise
in magnetoresistance is observed for high-entropy samples with the increase in
Sr concentration. These findings considering the configurational complexity of
different rare-earths advance the understanding of high-entropy rare earth
manganites. | 2212.00819v1 |
2018-03-02 | Tuning thermal transport in graphene via combinations of molecular antiresonances | We propose a method to engineer the phonon thermal transport properties of
low dimensional systems. The method relies on introducing a predetermined
combination of molecular adsorbates, which give rise to antiresonances at
frequencies specific to the molecular species. Despite their dissimilar
transmission spectra, thermal resistances due to individual molecules remain
almost the same for all species. On the other hand, thermal resistance due to
combinations of different species are not additive and show large differences
depending on the species. Using a toy model, the physics underlying the
violation of resistance summation rule is investigated. It is demonstrated that
equivalent resistance of two scatterers having the same resistances can be
close to the sum of the constituents or $\sim$70\% of it depending on the
relative positions of the antiresonances. The relative positions of the
antiresonances determine the net change in transmission, therefore the
equivalent resistance. Since the entire spectrum is involved in phonon spectrum
changes in different parts of the spectrum become important. Performing
extensive first-principles based computations, we show that these distinctive
attributes of phonon transport can be useful to tailor the thermal transport
through low dimensional materials, especially for thermoelectric and thermal
management applications. | 1803.01029v2 |
2017-01-15 | Thickness dependence of the resistivity of Platinum group metal thin films | We report on the thin film resistivity of several platinum-group metals (Ru,
Pd, Ir, Pt). Platinum-group thin films show comparable or lower resistivities
than Cu for film thicknesses below about 5\,nm due to a weaker thickness
dependence of the resistivity. Based on experimentally determined mean linear
distances between grain boundaries as well as ab initio calculations of the
electron mean free path, the data for Ru, Ir, and Cu were modeled within the
semiclassical Mayadas--Shatzkes model [Phys. Rev. B 1, 1382 (1970)] to assess
the combined contributions of surface and grain boundary scattering to the
resistivity. For Ru, the modeling results indicated that surface scattering was
strongly dependent on the surrounding material with nearly specular scattering
at interfaces with SiO2 or air but with diffuse scattering at interfaces with
TaN. The dependence of the thin film resistivity on the mean free path is also
discussed within the Mayadas--Shatzkes model in consideration of the
experimental findings. | 1701.04124v3 |
2022-08-04 | Topological Metal MoP Nanowire for Interconnect | The increasing resistance of Cu interconnects for decreasing dimensions is a
major challenge in continued downscaling of integrated circuits beyond the 7-nm
technology node as it leads to unacceptable signal delays and power consumption
in computing. The resistivity of Cu increases due to electron scattering at
surfaces and grain boundaries of the interconnects at the nanoscale.
Topological semimetals, owing to their topologically protected surface states
and suppressed electron backscattering, are promising material candidates to
potentially replace current Cu interconnects as low-resistance interconnects.
Here, we report the attractive resistivity scaling of topological metal MoP
nanowires and show that the resistivity values are comparable to those of Cu
interconnects below 500 nm$^2$ cross-section areas. More importantly, we
demonstrate that the dimensional scaling of MoP nanowires, in terms of line
resistance versus total cross-sectional area, is superior to those of effective
Cu and barrier-less Ru interconnects, suggesting MoP is an attractive solution
to the current scaling challenge of Cu interconnects. | 2208.02784v1 |
2008-04-04 | Magnetic Order versus superconductivity in the Iron-based layered La(O1-xFx)FeAs systems | In high-transition temperature (high-Tc) copper oxides, it is generally
believed that antiferromagnetism plays a fundamental role in the
superconducting mechanism because superconductivity occurs when mobile
electrons or holes are doped into the antiferromagnetic parent compounds. The
recent discovery of superconductivity in the rare-earth (R) iron-based oxide
systems [RO1-xFxFeAs] has generated enormous interest because these materials
are the first noncopper oxide superconductors with Tc exceeding 50 K. The
parent (nonsuperconducting) LaOFeAs material is metallic but shows anomalies
near 150 K in both resistivity and dc magnetic susceptibility. While optical
conductivity and theoretical calculations suggest that LaOFeAs exhibits a
spin-density-wave (SDW) instability that is suppressed with doping electrons to
form superconductivity, there has been no direct evidence of the SDW order.
Here we use neutron scattering to demonstrate that LaOFeAs undergoes an abrupt
structural distortion below ~150 K, changing the symmetry from tetragonal
(space group P4/nmm) to monoclinic (space group P112/n) at low temperatures,
and then followed with the development of long range SDW-type antiferromagnetic
order at ~134 K with a small moment but simple magnetic structure. Doping the
system with flourine suppresses both the magnetic order and structural
distortion in favor of superconductivity. Therefore, much like high-Tc copper
oxides, the superconducting regime in these Fe-based materials occurs in close
proximity to a long-range ordered antiferromagnetic ground state. Since the
discovery of long | 0804.0795v1 |
2012-12-11 | Characterization of thin-film NbN superconductor for single-photon detection by transport measurements | The fabrication of high-quality thin superconducting films is essential for
single-photon detectors. Their device performance is crucially affected by
their material parameters, thus requiring reliable and nondestructive
characterization methods after the fabrication and patterning processes.
Important material parameters to know are the resistivity, superconducting
transition temperature, relaxation time of quasiparticles, and uniformity of
patterned wires. In this work, we characterize micro-patterned thin NbN films
by using transport measurements in magnetic fields. We show that from the
instability of vortex motion at high currents in the flux-flow state of the
$IV$ characteristic, the inelastic life time of quasiparticles can be
determined to be about 2 ns. Additionally, from the depinning transition of
vortices at low currents, as a function of magnetic field, the size
distribution of grains can be extracted. This size distribution is found to be
in agreement with the film morphology obtained from scanning electron
microscopy and high-resolution transmission electron microscopy images. | 1212.2258v2 |
2014-12-11 | High-precision realization of robust quantum anomalous Hall state in a hard ferromagnetic topological insulator | The discovery of the quantum Hall (QH) effect led to the realization of a
topological electronic state with dissipationless currents circulating in one
direction along the edge of a two dimensional electron layer under a strong
magnetic field. The quantum anomalous Hall (QAH) effect shares a similar
physical phenomenon as the QH effect, whereas its physical origin relies on the
intrinsic spin-orbit coupling and ferromagnetism.Here we report the
experimental observation of the QAH state in V-doped (Bi,Sb)2Te3 films with the
zero-field longitudinal resistance down to 0.00013+-0.00007h/e2 (~3.35+-1.76
ohm), Hall conductance reaching 0.9998+-0.0006e2/h and the Hall angle becoming
as high as 89.993+-0.004degree at T=25mK. Further advantage of this system
comes from the fact that it is a hard ferromagnet with a large coercive field
(Hc>1.0T) and a relative high Curie temperature. This realization of robust QAH
state in hard FMTIs is a major step towards dissipationless electronic
applications without external fields. | 1412.3758v2 |
2015-01-22 | High spin polarization and large spin splitting in equiatomic quaternary CoFeCrAl Heusler alloy | In this paper, we investigate CoFeCrAl alloy by means of various experimental
techniques and ab-initio calculations to look for half-metallic nature. The
alloy is found to exist in the cubic Heusler structure, with presence of B2
ordering. Saturation magnetization (MS) value of about 2 Bohr magneton/f.u. is
observed at 8 K under ambient pressure, which is in good agreement with the
Slater-Pauling rule. MS values are found to be independent of pressure, which
is a prerequisite for half-metals. The ab-initio electronic structure
calculations predict half-metallic nature for the alloy with a spin slitting
energy of 0.31 eV. Importantly, this system shows a high current spin
polarization value of 0.67 [with error of 0.02], as deduced from the point
contact Andreev reflection (PCAR) measurements. Linear dependence of electrical
resistivity with temperature indicates the possibility of reasonably high spin
polarization at elevated temperatures (~150 K) as well. All these suggest that
CoFeCrAl is a promising material for the spintronic devices. | 1501.05599v1 |
2015-12-08 | A Two-Temperature Model of Magnetized Protostellar Outflows | We explore kinematics and morphologies of molecular outflows driven by young
protostars using magnetohydrodynamic simulations in the context of the unified
wind model of Shang et al. The model explains the observed high-velocity jet
and low-velocity shell features. In this work we investigate how these
characteristics are affected by the underlying temperature and magnetic field
strength. We study the problem of a warm wind running into a cold ambient
toroid by using a tracer field that keeps track of the wind material. While an
isothermal equation of state is adopted, the effective temperature is
determined locally based on the wind mass fraction. In the unified wind model,
the density of the wind is cylindrically stratified and highly concentrated
toward the outflow axis. Our simulations show that for a sufficiently
magnetized wind, the jet identity can be well maintained even at high
temperatures. However, for a high temperature wind with low magnetization, the
thermal pressure of the wind gas can drive material away from the axis, making
the jet less collimated as it propagates. We also study the role of the
poloidal magnetic field of the toroid. It is shown that the wind-ambient
interface becomes more resistant to corrugation when the poloidal field is
present, and the poloidal field that bunches up within the toroid prevents the
swept-up material from being compressed into a thin layer. This suggests that
the ambient poloidal field may play a role in producing a smoother and thicker
swept-up shell structure in the molecular outflow. | 1512.02609v1 |
2017-10-25 | Small-mass atomic defects enhance vibrational thermal transport at disordered interfaces with ultrahigh thermal boundary conductance | The role of interfacial nonidealities and disorder on thermal transport
across interfaces is traditionally assumed to add resistance to heat transfer,
decreasing the thermal boundary conductance (TBC).$^1$ However, recent
computational works have suggested that interfacial defects can enhance this
thermal boundary conductance through emergence of unique vibrations that are
intrinsic to the material interface and defect atoms,$^{2-6}$ a finding that
contradicts traditional theory and conventional understanding. By manipulating
the local heat flux of atomic vibrations that comprise these interfacial modes,
in principle, the TBC can be increased. In this work, we provide evidence that
interfacial defects can enhance the TBC across interfaces through the emergence
of unique high frequency vibrational modes that arise from atomic mass defects
at the interface with relatively small masses. We demonstrate ultrahigh TBC at
amorphous SiOC:H/SiC:H interfaces, approaching 1 GW m$^{-2}$ K$^{-1}$, that is
further increased through the introduction of nitrogen defects. The fact that
disordered interfaces can exhibit such high conductances, which can be further
increased with additional defects offers a unique direction in controlling
interfacial thermal transport that becomes important in manipulating heat
transfer across materials with high densities of interfaces. | 1710.09440v1 |
2019-03-14 | Nonsaturating large magnetoresistance in the high carrier density nonsymmorphic metal CrP | The band structure of high carrier density metal CrP features an interesting
crossing at the Y point of the Brillouin zone. The crossing, which is protected
by the nonsymmorphic symmetry of the space group, results in a hybrid,
semi-Dirac-like energy-momentum dispersion relation near Y. The linear
energy-momentum dispersion relation along Y-$\Gamma$ is reminiscent of the
observed band structure in several semimetallic extremely large
magnetoresistance (XMR) materials. We have measured the transverse
magnetoresistance of CrP up to 14 T at temperatures as low as $\sim$ 16 mK. Our
data reveal a nonsaturating, quadratic magnetoresistance as well as the
behaviour of the so-called `turn-on' temperature in the temperature dependence
of resistivity. Despite the difference in the magnitude of the
magnetoresistance and the fact that CrP is not a semimetal, these features are
qualitatively similar to the observations reported for XMR materials. Thus, the
high-field electrical transport studies of CrP offer the prospect of
identifying the possible origin of the nonsaturating, quadratic
magnetoresistance observed in a wide range of metals. | 1903.05914v1 |
2018-07-03 | An Inside Look at the Ti-MoS2 Contact in Ultra-thin Field Effect Transistor with Atomic Resolution | Two-dimensional molybdenum disulfide (MoS2) is an excellent channel material
for ultra-thin field effect transistors. However, high contact resistance
across the metal-MoS2 interface continues to limit its widespread realization.
Here, using atomic-resolution analytical scanning transmission electron
microscopy (STEM) together with first principle calculations, we show that this
contact problem is a fundamental limitation from the bonding and interactions
at the metal-MoS2 interface that cannot be solved by improved deposition
engineering. STEM analysis in conjunction with theory shows that when MoS2 is
in contact with Ti, a metal with a high affinity to form strong bonds with
sulfur, there is a release of S from Mo along with the formation of small
Ti/TixSy clusters. A destruction of the MoS2 layers and penetration of metal
can also be expected. The design of true high-mobility metal-MoS2 contacts will
require the optimal selection of the metal or alloy based on their bonding
interactions with the MoS2 surface. This can be advanced by evaluation of
binding energies with increasing the number of atoms within metal clusters. | 1807.01377v1 |
2021-02-03 | Novel drying additives and their evaluation for self-flowing refractory castables | The drying step of dense refractory castables containing hydraulic binders is
a critical process, which usually requires using slow heating rates due to the
high explosion trend of such materials during their first thermal treatment.
Thus, this work investigated the performance of alternative additives to induce
faster and safer drying of self-flowing high-alumina refractory castables
bonded with calcium aluminate cement (CAC) or hydratable alumina (HA). The
following materials were analyzed for this purpose: polymeric fibers, a
permeability enhancing compound (RefPac MIPORE 20) and an organic additive
(aluminum salt of 2-hydroxypropanoic acid). The drying behavior and explosion
resistance of the cured samples were evaluated when subjecting the prepared
castables to heating rates of 2, 5 or 20C/min and the obtained data were then
correlated to the potential of the drying agents to improve the permeability
and mechanical strength level of the refractories at different temperatures.
The collected results attested that the selected additives were more efficient
in optimizing the drying behavior of the CAC-bonded compositions, whereas the
HA-containing castables performed better when the aluminum-based salt was
blended with a small amount of CAC (0.5 wt.%), which changed the binders
hydration reaction sequence and optimized the permeability level of the
resulting microstructure. Consequently, some of the designed compositions
evaluated in this work showed improved drying behavior and no explosion was
observed even during the tests carried out under a high heating rate (20C/min). | 2102.02008v1 |
2021-02-06 | Contact-Barrier Free, High Mobility, Dual-Gated Junctionless Transistor Using Tellurium Nanowire | Gate-all-around nanowire transistor, due to its extremely tight electrostatic
control and vertical integration capability, is a highly promising candidate
for sub-5 nm technology node. In particular, the junctionless nanowire
transistors are highly scalable with reduced variability due to avoidance of
steep source/drain junction formation by ion implantation. Here we demonstrate
a dual-gated junctionless nanowire \emph{p}-type field effect transistor using
tellurium nanowire as the channel. The dangling-bond-free surface due to the
unique helical crystal structure of the nanowire, coupled with an integration
of dangling-bond-free, high quality hBN gate dielectric, allows us to achieve a
phonon-limited field effect hole mobility of $570\,\mathrm{cm^{2}/V\cdot s}$ at
270 K, which is well above state-of-the-art strained Si hole mobility. By
lowering the temperature, the mobility increases to
$1390\,\mathrm{cm^{2}/V\cdot s}$ and becomes primarily limited by Coulomb
scattering. \txc{The combination of an electron affinity of $\sim$4 eV and a
small bandgap of tellurium provides zero Schottky barrier height for hole
injection at the metal-contact interface}, which is remarkable for reduction of
contact resistance in a highly scaled transistor. Exploiting these properties,
coupled with the dual-gated operation, we achieve a high drive current of
$216\,\mathrm{\mu A/\mu m}$ while maintaining an on-off ratio in excess of
$2\times10^4$. The findings have intriguing prospects for alternate channel
material based next-generation electronics. | 2102.03507v1 |
2021-05-27 | Route to High-Performance Micro-solid Oxide Fuel Cells on Metallic Substrates | Micro-solid oxide fuel cells based on thin films have strong potential for
use in portable power devices. However, devices based on silicon substrates
typically involve thin-film metallic electrodes which are unstable at high
temperatures. Devices based on bulk metal substrates overcome these
limitations, though performance is hindered by the challenge of growing
state-of-the-art epitaxial materials on metals. Here, we demonstrate for the
first time the growth of epitaxial cathode materials on metal substrates
(stainless steel) commercially supplied with epitaxial electrolyte layers (1.5
{um (Y2O3)0.15(ZrO2)0.85 (YSZ) + 50 nm CeO2). We create epitaxial mesoporous
cathodes of (La0.60Sr0.40)0.95Co0.20Fe0.80O3 (LSCF) on the substrate by growing
LSCF/MgO vertically aligned nanocomposite films by pulsed laser deposition,
followed by selectively etching out the MgO. To enable valid comparison with
the literature, the cathodes are also grown on single-crystal substrates,
confirming state-of-the-art performance with an area specific resistance of
100ohmegacm2 at 500dC and activation energy down to 0.97 eV. The work marks an
important step toward the commercialization of high-performance micro-solid
oxide fuel cells for portable power applications. | 2105.13117v1 |
2023-03-15 | Characterization of local deformation around hydrides in Zircaloy-4 using conventional and high angular resolution electron backscatter diffraction | Zircaloy-4 is used as a fuel cladding material for water reactors, as it has
good mechanical properties, corrosion resistance, and a low thermal neutron
absorption cross section. However, the mechanical performance of Zircaloy-4 can
be reduced during service due to hydrogen uptake and hydride formation. These
hydrides are brittle, and often reduce the strength and toughness of materials
as well as increase susceptibility to delayed hydride cracking (DHC). In this
work, large grain Zircaloy-4 with hydrides was prepared and then cross
sectioned using cryo-ion beam polishing, using plasma focused ion beam (pFIB)
and broad ion beam (BIB) approaches to enable the preparation of a very high
quality flat surface with no preferential etching of either the hydride or
zirconium metal (typically metallographic polishing preferentially removes
hydrides). Conventional and high angular resolution electron backscatter
diffraction (EBSD) analysis were then used to explore morphology, deformation
fields, and orientation relationships between the zirconium matrix and
hydrides. Four maps were collected for analysis which included hydrides near
grain boundaries: (a) where the hydride smoothly decorates across two of the
connecting boundaries near a triple junction; (b) where the hydride smoothly
decorates the boundary; (c) a mixture of smooth decoration of the interface and
protrusion into the grains; (d) fine scale hydride that protrudes into one
grain. This work highlights that incompatibility of the hydride within the
zirconium matrix is strongly linked to the orientation relationship of the
hydride and matrix, and the grain boundary character. These results may enable
enhanced understanding of the role of hydrides in fracture as well as
stress-induced hydride reorientation and DHC susceptibility. | 2303.08311v1 |
2014-10-15 | Cyclic Strength and Nonlinear Material Fracture Mechanics (by the example of steels) | It was shown that a material fatigue fracture diagram can be viewed as a
locus of points with $\sigma $ and $\sqrt l$ coordinates' product equal to
$K_{1c}/2$, and $\sigma $ and $l$ product -- to $G_{1c}/2$, where $K_{1c}$ and
$G_{1c}$ are non-linear fracture mechanics force and energy criteria. It was
established that the average number of interatomic bonds destroyed within one
alternate stress $\nabla_{1cs}$ cycle is directly proportional to $\sigma $
that is twice as large as a peak value of $\sigma^a$. It was found that
low-cycle fatigue is characterized by $\sigma >\sigma_{0.2}$ and $\sigma_{1cs}>
1$, high-cycle fatigue -- by $\sigma = \sigma_{0.2}$ and $\nabla_{1cs} = 1$,
and giga-cycle fatigue -- by $\sigma < \sigma_{0.2}$ and $\nabla_{1cs} < 1$. An
individual interatomic bond cannot be destroyed part by part but as a single
unit. The latter means that in giga-cycle fatigue a single interatomic bond is
destroyed within several cycles rather than within a single cycle. The factors
$F$ (collapsibility) and $R$ (resistibility) were proposed and mentioned as
essential material physical constants. The introduced notion $\nabla_{1cs}$ and
the established linear nature of $\nabla_{1cs}$ relationship allow to: a)
clarify the fatigue crack growth physical nature in low-, high- and giga-cycle
fracture zones; b) determine the nature of a fatigue fracture diagram
disruption; c) plot the fatigue fracture diagram using the results obtained in
a single specimen cyclic strength test with a selected value of $\sigma \ge
\sigma_{0.2}$. For giga-cycle fatigue it is important (with similar purpose in
mind) to determine this dependence for $\sigma < \sigma_{0.2}$. It is
recommended to use $G_{1c}$ criterion to find the $l_{cr}$ length value which
in contrast to $K_{1c}$ has a clear physical nature. | 1410.4177v2 |
2014-12-14 | Gate-tunable quantum oscillations in ambipolar Cd3As2 thin films | Electrostatic doping in materials can lead to various exciting electronic
properties, such as metal-insulator transition and superconductivity, by
altering the Fermi level position or introducing exotic phases. Cd3As2, a
three-dimensional (3D) analog of graphene with extraordinary carrier mobility,
was predicted to be a 3D Dirac semimetal, a feature confirmed by recent
experiments. However, most research so far has been focused on metallic bulk
materials that are known to possess ultra-high mobility and giant
magnetoresistance but limited carrier transport tunability. Here, we report on
the first observation of a gate-induced transition from band conduction to
hopping conduction in single-crystalline Cd3As2 thin films via electrostatic
doping by solid electrolyte gating. The extreme charge doping enables the
unexpected observation of p-type conductivity in a 50 nm-thick Cd3As2 thin film
grown by molecular beam epitaxy. More importantly, the gate-tunable
Shubnikov-de Haas (SdH) oscillations and the temperature-dependent resistance
reveal a unique band structure and bandgap opening when the dimensionality of
Cd3As2 is reduced. This is also confirmed by our first-principles calculations.
The present results offer new insights towards nanoelectronic and
optoelectronic applications of Dirac semimetals in general, and provide new
routes in the search for the intriguing quantum spin Hall effect in
low-dimension Dirac semimetals, an effect that is theoretically predicted but
not yet experimentally realized. | 1412.4380v2 |
2016-05-15 | Nearly massless Dirac fermions hosted by Sb square net in BaMnSb2 | Layered compounds AMnBi2 (A=Ca, Sr, Ba, or rare earth element) have been
established as Dirac materials. Dirac electrons generated by the
two-dimensional (2D) Bi square net in these materials are normally massive due
to the presence of a spin-orbital coupling (SOC) induced gap at Dirac nodes.
Here we report that the Sb square net in an isostructural compound BaMnSb2 can
host nearly massless Dirac fermions. We observed strong Shubnikov-de Haas (SdH)
oscillations in this material. From the analyses of the SdH oscillations, we
find key signatures of Dirac fermions, including light effective mass
(~0.052m0; m0, mass of free electron), high quantum mobility (1280 cm2V-1S-1)
and a Pi Berry phase accumulated along cyclotron orbit. Compared with AMnBi2,
BaMnSb2 also exhibits much more significant quasi two-dimensional (2D)
electronic structure, with the out-of-plane transport showing nonmetallic
conduction below 120K and the ratio of the out-of-plane and in-plane
resistivity reaching ~670. Additionally, BaMnSb2 also exhibits an
antiferromagnetic order with a weak ferromagnetic component. The combination of
nearly massless Dirac fermions on quasi-2D planes with a magnetic order makes
BaMnSb2 an intriguing platform for seeking novel exotic phenomena of massless
Dirac electrons. | 1605.04613v2 |
2017-10-09 | Huge magnetoresistance and ultra-sharp metamagnetic transition in polycrystalline ${Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3}$ | Large magnetoresistive materials are of immense interest for a number of
spintronic applications by developing high density magnetic memory devices,
magnetic sensors and magnetic switches. Colossal magnetoresistance, for which
resistivity changes several order of magnitude (${\sim10^4 \%}$) in an external
magnetic field, occurs mainly in phase separated oxide materials, namely
manganites, due to the phase competition between the ferromagnetic metallic and
the antiferromagnetic insulating regions. Can one further enhance the
magnetoresistance by tuning the volume fraction of the two phases? In this
work, we report a huge colossal magnetoresistance along with the ultra-sharp
metamagnetic transition in half doped ${Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3}$
manganite compound by suitably tuning the volume fraction of the competing
phases. The obtained magnetoresistance value at 10 K is as large as
$\sim10^{13}\%$ in a 30 kOe external magnetic field and $\sim10^{15}\%$ in 90
kOe external magnetic field and is several orders of magnitude higher than any
other observed magnetoresistance value reported so far. Using model Hamiltonian
calculations we have shown that the inhomogeneous disorder, deduced from
tunneling electron microscopy, suppresses the CE-type phase and seeds the
ferromagnetic metal in an external magnetic field. | 1710.03007v2 |
2018-09-12 | V$_5$S$_8$: a Kondo lattice based on intercalation of van der Waals layered transition metal dichalcogenide | Since the discovery of graphene, a tremendous amount of two dimensional (2D)
materials have surfaced. Their electronic properties can usually be well
understood without considering correlations between electrons. On the other
hand, strong electronic correlations are known to give rise to a variety of
exotic properties and new quantum phases, for instance, high temperature
superconductivity, heavy fermions and quantum spin liquids. The study of these
phenomena has been one of the main focuses of condensed matter physics. There
is a strong incentive to introduce electronic correlations into 2D materials.
Via intercalating a van der Waals layered compound VS$_2$, we show an emergence
of a Kondo lattice, an extensively studied strongly correlated system, by
magnetic, specific heat, electrical and thermoelectric transport studies. In
particular, an exceptionally large Sommerfeld coefficient, 440
mJ$\cdot$K$^{-2}\cdot$mol$^{-1}$, indicates a strong electron correlation. The
obtained Kadowaki-Woods ratio, $2.7\times 10^{-6}$
$\mu\Omega\cdot$cm$\cdot$mol$^2\cdot$K$^2\cdot$mJ$^{-2}$, also supports the
strong electron-electron interaction. The temperature dependence of the
resistivity and thermopower corroborate the Kondo lattice picture. The
intercalated compound is one of a few rare examples of $d$-electron Kondo
lattices. We further show that the Kondo physics persists in ultra-thin films.
This work thus demonstrates a route to generate strong correlations in 2D
materials. | 1809.04213v1 |
2014-08-03 | Carrier screening, transport, and relaxation in 3D Dirac semimetals | A theory is developed for the density and temperature dependent carrier
conductivity in doped three-dimensional (3D) Dirac materials focusing on
resistive scattering from screened Coulomb disorder due to random charged
impurities (e.g., dopant ions and unintentional background impurities). The
theory applies both in the undoped intrinsic ("high-temperature", $T \gg T_F$)
and the doped extrinsic ("low-temperature", $T \ll T_F$) limit with analytical
scaling properties for the carrier conductivity obtained in both regimes, where
$T_F$ is the Fermi temperature corresponding to the doped free carrier density
(electrons or holes). The scaling properties describing how the conductivity
depends on the density and temperature can be used to establish the Dirac
nature of 3D systems through transport measurements. We also consider the
temperature dependent conductivity limited by the acoustic phonon scattering in
3D Dirac materials. In addition, we theoretically calculate and compare the
single particle relaxation time $\tas$, defining the quantum level broadening,
and the transport scattering time $\tat$, defining the conductivity, in the
presence of screened charged impurity scattering. A critical quantitative
analysis of the $\tat/\tas$ results for 3D Dirac materials in the presence of
long-range screened Coulomb disorder is provided. | 1408.0518v2 |
2017-03-28 | Metallic vanadium disulfide nanosheets as a platform material for multifunctional electrode applications | Nano-thick metallic transition metal dichalcogenides such as VS$_{2}$ are
essential building blocks for constructing next-generation electronic and
energy-storage applications, as well as for exploring unique physical issues
associated with the dimensionality effect. However, such 2D layered materials
have yet to be achieved through either mechanical exfoliation or bottom-up
synthesis. Herein, we report a facile chemical vapor deposition route for
direct production of crystalline VS$_{2}$ nanosheets with sub-10 nm thicknesses
and domain sizes of tens of micrometers. The obtained nanosheets feature
spontaneous superlattice periodicities and excellent electrical conductivities
(~3$\times$10$^{3}$ S cm$^{-1}$), which has enabled a variety of applications
such as contact electrodes for monolayer MoS$_{2}$ with contact resistances of
~1/4 to that of Ni/Au metals, and as supercapacitor electrodes in aqueous
electrolytes showing specific capacitances as high as 8.6$\times$10$^{2}$ F
g$^{-1}$. This work provides fresh insights into the delicate
structure-property relationship and the broad application prospects of such
metallic 2D materials. | 1703.09582v1 |
2019-02-26 | Superconductivity at 161 K in Thorium Hydride $ThH_{10}$: Synthesis and Properties | Here we report targeted high-pressure synthesis of two novel high-$T_C$
hydride superconductors, $P6_3/mmc$-$ThH_9$ and $Fm\bar{3}m$-$ThH_{10}$, with
the experimental critical temperatures ($T_C$) of 146 K and 159-161 K and upper
critical magnetic fields ($\mu$$H_C$) 38 and 45 Tesla at pressures 170-175
Gigapascals, respectively. Superconductivity was evidenced by the observation
of zero resistance and a decrease of $T_C$ under external magnetic field up to
16 Tesla. This is one of the highest critical temperatures that has been
achieved experimentally in any compounds, along with such materials as
$LaH_{10}$, $H_3S$ and $HgBa_2Ca_xCu_2O_{6+z}$. Our experiments show that
$fcc$-$ThH_{10}$ has stabilization pressure of 85 GPa, making this material
unique among all known high-$T_C$ metal polyhydrides. Two recently predicted
Th-H compounds, $I4/mmm$-$ThH_4$ (> 86 GPa) and $Cmc2_1$-$ThH_6$ (86-104 GPa),
were also synthesized. Equations of state of obtained thorium polyhydrides were
measured and found to perfectly agree with the theoretical calculations. New
phases were examined theoretically and their electronic, phonon, and
superconducting properties were calculated. | 1902.10206v4 |
2022-02-10 | Giant magnetoresistance, Fermi surface topology, Shoenberg effect and vanishing quantum oscillations in type-II Dirac semimetal candidates MoSi$_2$ and WSi$_2$ | We performed comprehensive theoretical and experimental studies of the
electronic structure and the Fermi surface topology of two novel quantum
materials, MoSi$_2$ and WSi$_2$. The theoretical predictions of the electronic
structure in the vicinity of the Fermi level was verified experimentally by
thorough analysis of the observed quantum oscillations in both electrical
resistivity and magnetostriction. We established that the Fermi surface sheets
in MoSi$_2$ and WSi$_2$ consist of 3D dumbbell-shaped hole-like pockets and
rosette-shaped electron-like pockets, with nearly equal volumes. Based on this
finding, both materials were characterized as almost perfectly compensated
semimetals. In conjunction, the magnetoresistance attains giant values of
$10^4$ and $10^5\,\%$ for WSi$_2$ and MoSi$_2$, respectively. In turn, the
anisotropic magnetoresistance achieves $-95$ and $-98\,\%$ at $T=2\,$K and in
$B=14\,$T for WSi$_2$ and MoSi$_2$, respectively. Furthermore, for both
compounds we observed the Shoenberg effect in their Shubnikov-de Haas
oscillations that persisted at as high temperature as $T=25\,$K in MoSi$_2$ and
$T=12\,$K in WSi$_2$. In addition, we found for MoSi$_2$ a rarely observed
spin-zero phenomenon. Remarkably, the electronic structure calculations
revealed type-II Dirac cones located near 480 meV and 710 meV above the Fermi
level in MoSi$_2$ and WSi$_2$, respectively. | 2202.05362v1 |
2017-04-24 | 1D van der Waals Material Tellurium: Raman Spectroscopy under Strain and Magneto-transport | Experimental demonstrations of 1D van der Waals material tellurium have been
presented by Raman spectroscopy under strain and magneto-transport. Raman
spectroscopy measurements have been performed under strains along different
principle axes. Pronounced strain response along c-axis is observed due to the
strong intra-chain covalent bonds, while no strain response is obtained along
a-axis due to the weak inter-chain van der Waals interaction. Magneto-transport
results further verify its anisotropic property, resulting in dramatically
distinct magneto-resistance behaviors in terms of three different magnetic
field directions. Specifically, phase coherence length extracted from weak
antilocalization effect, L$_{\Phi}$ ~ T$^{-0.5}$, claims its 2D transport
characteristics when an applied magnetic field is perpendicular to the thin
film. In contrast, L$_{\Phi}$ ~ T$^{-0.33}$ is obtained from universal
conductance fluctuations once the magnetic field is along c-axis of Te,
indicating its nature of 1D transport along the helical atomic chains. Our
studies, which are obtained on high quality single crystal tellurium thin film,
appear to serve as strong evidences of its 1D van der Waals structure from
experimental perspectives. It is the aim of this paper to address this special
concept that differs from the previous well-studied 1D nanowires or 2D van der
Waals materials. | 1704.07020v1 |
2019-03-09 | A New Magnetic Topological Quantum Material Candidate by Design | Magnetism, when combined with an unconventional electronic band structure,
can give rise to forefront electronic properties such as the quantum anomalous
Hall effect, axion electrodynamics, and Majorana fermions. Here we report the
characterization of high-quality crystals of EuSn$_2$P$_2$, a new quantum
material specifically designed to engender unconventional electronic states
plus magnetism. EuSn$_2$P$_2$ has a layered, Bi$_2$Te$_3$-type structure.
Ferromagnetic interactions dominate the Curie-Weiss susceptibility, but a
transition to antiferromagnetic ordering occurs near 30 K. Neutron diffraction
reveals that this is due to two-dimensional ferromagnetic spin alignment within
individual Eu layers and antiferromagnetic alignment between layers - this
magnetic state surrounds the Sn-P layers at low temperatures. The bulk
electrical resistivity is sensitive to the magnetism. Electronic structure
calculations reveal that EuSn$_2$P$_2$ might be a strong topological insulator,
which can be a new magnetic topological quantum material (MTQM) candidate. The
calculations show that surface states should be present, and they are indeed
observed by ARPES measurements. | 1903.03888v1 |
2019-01-23 | Enhancing Interconnect Reliability and Performance by Converting Tantalum to 2D Layered Tantalum Sulfide at Low Temperature | The interconnect half-pitch size will reach ~20 nm in the coming sub-5 nm
technology node. Meanwhile, the TaN/Ta (barrier/liner) bilayer stack has to be
> 4 nm to ensure acceptable liner and diffusion barrier properties. Since
TaN/Ta occupy a significant portion of the interconnect cross-section and they
are much more resistive than Cu, the effective conductance of an ultra-scaled
interconnect will be compromised by the thick bilayer. Therefore, two
dimensional (2D) layered materials have been explored as diffusion barrier
alternatives. However, many of the proposed 2D barriers are prepared at too
high temperatures to be compatible with the back-end-of-line (BEOL) technology.
In addition, as important as the diffusion barrier properties, the liner
properties of 2D materials must be evaluated, which has not yet been pursued.
Here, a 2D layered tantalum sulfide (TaSx) with ~1.5 nm thickness is developed
to replace the conventional TaN/Ta bilayer. The TaSx ultra-thin film is
industry-friendly, BEOL-compatible, and can be directly prepared on
dielectrics. Our results show superior barrier/liner properties of TaSx
compared to the TaN/Ta bilayer. This single-stack material, serving as both a
liner and a barrier, will enable continued scaling of interconnects beyond 5 nm
node. | 1901.08143v1 |
2020-08-31 | Enhanced fracture toughness in ceramic superlattice thin films: on the role of coherency stresses and misfit dislocations | Superlattice (SL) thin films composed of refractory ceramics unite extremely
high hardness and enhanced fracture toughness; a material combination often
being mutually exclusive. While the hardness enhancement obtained whentwo
materials form a superlattice is well described by existing models based on
dislocation mobility, the underlying mechanisms behind the increase in fracture
toughness are yet to be unraveled. Here we provide a model based on linear
elasticity theory to predict the fracture toughness enhancement in
(semi-)epitaxial nanolayers due to coherency stresses and formation of misfit
dislocations. We exemplarily study a superlattice structure composed of two
cubic transition metal nitrides (TiN, CrN) on a MgO (100) single-crystal
substrate. Minimization of the overall strain energy, each time a new layer is
added on the nanolayered stack, allows estimating the density of misfit
dislocations formed at the interfaces. The evolving coherency stresses, which
are partly relaxed by the misfit dislocations, are then used to calculate the
apparent fracture toughness of respective SL architectures by applying the
weight function method. The results show that the critical stress intensity
increases steeply with increasing bilayer period for very thin (essentially
dislocation-free) SLs, before the K_IC values decline more gently along with
the formation of misfit dislocations. The characteristic K_IC vs.
bilayer-period-dependence nicely matches experimental trends. Importantly, all
critical stress intensity values of the superlattice films clearly exceed the
intrinsic fracture toughness of the constituting layer materials, evincing the
importance of coherency stresses for increasing the crack growth resistance. | 2008.13652v1 |
2020-12-10 | Evidence of non-trivial Berry phase and Kondo physics in SmBi | Realization of semimetals with non-trivial topologies such as Dirac and Weyl
semimetals, have provided a boost in the study of these quantum materials.
Presence of electron correlation makes the system even more exotic due to
enhanced scattering of charge carriers, Kondo screening etc. Here, we studied
the electronic properties of single crystalline, SmBi employing varied state of
the art bulk measurements. Magnetization data reveals two magnetic transitions;
an antiferromagnetic order with a Neel temperature of ~ 9 K and a second
magnetic transition at a lower temperature (= 7 K). The electrical resistivity
data shows an upturn typical of a Kondo system and the estimated Kondo
temperature is found to be close to the Neel temperature. High quality of the
crystal enabled us to discover signature of quantum oscillation in the
magnetization data even at low magnetic field. Using a Landau level fan diagram
analysis, a non-trivial Berry phase is identified for a Fermi pocket revealing
the topological character in this material. These results demonstrate an unique
example of the Fermiology in the antiferromagnetic state and opens up a new
paradigm to explore the Dirac fermion physics in correlated topological metal
via interplay of Kondo interaction, topological order and magnetism. | 2012.05459v1 |
2021-03-25 | Bonding nature and optical contrast of $TiTe_2$/$Sb_2Te_3$ phase-change heterostructure | Chalcogenide phase-change materials (PCMs) are regarded as the leading
candidate for storage-class non-volatile memory and neuro-inspired computing.
Recently, using the $TiTe_2$/$Sb_2Te_3$ material combination, a new framework -
phase-change heterostructure (PCH), has been developed and proved to
effectively suppress the noise and drift in electrical resistance upon memory
programming, largely reducing the inter-device variability. However, the
atomic-scale structural and chemical nature of PCH remains to be fully
understood. In this work, we carry out thorough ab initio simulations to assess
the bonding characteristics of the PCH. We show that the $TiTe_2$ crystalline
nanolayers do not chemically interact with the surrounding $Sb_2Te_3$, and are
stabilized by strong covalent and electrostatic Ti-Te interactions, which
create a prohibitively high barrier for atomic migrations along the pulsing
direction. We also find significant contrast in computed dielectric functions
in the PCH, suggesting possible optical applications of this class of devices.
With the more confined space and therefore constrained phase transition
compared to traditional PCM devices, the recently introduced class of PCH-based
devices may lead to improvements in phase-change photonic and optoelectronic
applications with much lower stochasticity during programming. | 2103.13583v2 |
2021-06-30 | Classifying charge carrier interaction in highly-compressed elements and silane | Since pivotal experimental discovery of the near-room-temperature
superconductivity (NRTS) in highly-compressed sulphur hydride by Drozdov et al
(2015 Nature 525 73-76), more than a dozen of binary and of ternary
hydrogen-rich phases exhibited superconducting transition above 100 K have been
discovered to date. There is a widely accepted theoretical point of view that
primary mechanism governing the emergence of superconductivity in hydrogen-rich
phases is the electron-phonon pairing. However, our recent analysis of
experimental temperature dependent resistance in $H_{3}S$, $LaH_{x}$, $PrH_{9}$
and $BaH_{12}$ (arXiv: 2104.14145) showed that these compounds exhibit the
dominance of non-electron-phonon charge carrier interaction and, thus, it is
unlikely that the electron-phonon pairing is the primary mechanism for the
emergence of superconductivity in these materials. Here we use the same
approach to reveal charge carrier interaction in highly-compressed lithium,
black phosphorous, sulfur, and silane. We found that all these superconductors
exhibit the dominance of non-electron-phonon charge carrier interaction. This
explains the failure of high-Tc values predicted for these materials by the
first-principles calculations which utilized the electron-phonon pairing as the
mechanism for the emergence of superconductivity in these materials. Our result
implies that alternative pairing mechanisms (i.e., electron-magnon,
electron-polaron, electron-electron, etc.) should be tested within
first-principles calculations approach as possible mechanisms for the emergence
of superconductivity in highly-compressed superconductors. | 2106.15873v1 |
2021-09-08 | Coherent spin rotation-induced zero thermal expansion in MnCoSi-based spiral magnets | Materials exhibiting zero thermal expansion (ZTE), namely, volume invariance
during temperature change, can resist thermal shock and are highly desired in
modern industries as high-precision components. However, pure ZTE materials are
rare, especially those that are metallic. Here, we report the discovery of a
pure metallic ZTE material: an orthorhombic Mn1-xNixCoSi spiral magnet. The
introduction of Ni can efficiently enhance the ferromagnetic exchange
interaction and construct the transition from a spiral magnetic state to a
ferromagnetic-like state in MnCoSi-based alloys. Systematic in situ neutron
powder diffraction revealed a new cycloidal spiral magnetic structure in bc
plane at ground state which would transform to the helical spiral in the ab
plane with increasing temperature. Combined with Lorentz transmission electron
microscopy techniques, the cycloidal and helical spin order coherently rotated
at varying periods along the c axis during the magnetic transition. This spin
rotation drove the continuous movement of the coupled crystalline lattice and
induced a large negative thermal expansion along the a axis, eventually leading
to a wide-temperature ZTE effect. Our work not only introduces a new ZTE alloy
but also presents a new mechanism by which to discover or design ZTE magnets. | 2109.03557v1 |
2022-04-09 | Role of substrate surface morphology on the performance of graphene inks for flexible electronics | Two-dimensional (2D) materials, such as graphene, are seen as potential
candidates for fabricating electronic devices and circuits on flexible
substrates. Inks or dispersions of 2D materials can be deposited on flexible
substrates by large-scale coating techniques, such as inkjet printing and spray
coating. One of the main issues in coating processes is nonuniform deposition
of inks, which may lead to large variations of properties across the
substrates. Here, we investigate the role of surface morphology on the
performance of graphene ink deposited on different paper substrates with
specific top coatings. Substrates with good wetting properties result in
reproducible thin films and electrical properties with low sheet resistance.
The correct choice of surface morphology enables high-performance films without
postdeposition annealing or treatment. Scanning terahertz time-domain
spectroscopy (THz-TDS) is introduced to evaluate both the uniformity and the
local conductivity of graphene inks on paper. A paper-based strain gauge is
demonstrated and a variable resistor acts as an on-off switch for operating an
LED. Customized surfaces can thus help in unleashing the full potential of
ink-based 2D materials. | 2204.04503v1 |
2023-04-28 | First-principles Prediction of Potential Candidate Materials MCu$_3$X$_4$ (M = V, Nb, Ta; X = S, Se, Te) for Neuromorphic Computing | Inspired by the neuro-synaptic frameworks in the human brain, neuromorphic
computing is expected to overcome the bottleneck of traditional von-Neumann
architecture and be used in artificial intelligence. Here, we predict a class
of potential candidate materials, MCu$_3$X$_4$ (M = V, Nb, Ta; X = S, Se, Te),
for neuromorphic computing applications through first-principles calculations
based on density functional theory. We find that when MCu$_3$X$_4$ are inserted
with Li atom, the systems would transform from semiconductors to metals due to
the considerable electron filling [~0.8 electrons per formula unit (f.u.)] and
still maintain well structural stability. Meanwhile, the inserted Li atom also
has a low diffusion barrier (~0.6 eV/f.u.), which ensures the feasibility to
control the insertion/extraction of Li by gate voltage. These results establish
that the system can achieve the reversible switching between two stable memory
states, i.e., high/low resistance state, indicating that it could potentially
be used to design synaptic transistor to enable neuromorphic computing. Our
work provides inspiration for advancing the search of candidate materials
related to neuromorphic computing from the perspective of theoretical
calculations. | 2304.14897v1 |
2023-06-26 | Microscopic conductivity of passive films on ferritic stainless steel for hydrogen fuel cells | Hydrogen fuel cells offer a clean and sustainable energy conversion solution.
The bipolar separator plate, a critical component in fuel cells, plays a vital
role in preventing reactant gas cross-contamination and facilitating efficient
ion transport in a fuel cell. High chromium ferritic stainless steel with an
artificially formed thin chromium oxide passive film has recently gained
attention due to its superior electrical conductivity and corrosion resistance,
making it a suitable material for separators. In this study, we investigate the
microscopic electrical conductivity of the intrinsic passive oxide film on such
ferritic stainless steel. Through advanced surface characterization techniques
such as current sensing atomic force microscopy and scanning tunneling
microscopy/spectroscopy, we discover highly conductive regions within the film
that vary depending on location. These findings provide valuable insights into
the behavior of the passive oxide film in fuel cells. By understanding the
microscopic electrical properties, we can enhance the design and performance of
separator materials in hydrogen fuel cells. Ultimately, this research
contributes to a broader understanding of separator materials and supports the
wider application of hydrogen fuel cells. | 2306.14513v1 |
2003-10-20 | Radiation induced oscillatory Hall effect in high mobility GaAs/AlGaAs devices | We examine the radiation induced modification of the Hall effect in high
mobility GaAs/AlGaAs devices that exhibit vanishing resistance under microwave
excitation. The modification in the Hall effect upon irradiation is
characterized by (a) a small reduction in the slope of the Hall resistance
curve with respect to the dark value, (b) a periodic reduction in the magnitude
of the Hall resistance, $R_{xy}$, that correlates with an increase in the
diagonal resistance, $R_{xx}$, and (c) a Hall resistance correction that
disappears as the diagonal resistance vanishes. | 0310474v2 |
2015-09-03 | A simple model for in- and out-of-plane resistivities of hole doped cuprates | The highly anisotropic and qualitatively different nature of in- and
out-of-plane charge dynamics in high-Tc cuprates cannot be accommodated within
the conventional Boltzmann transport theory. The variation of in- and
out-of-plane resistivities with temperature and hole content are also anomalous
and cannot be explained by Fermi-liquid theory. In this study we have proposed
a simple phenomenological model for the dc resistivity of cuprates by
incorporating two firmly established generic features of all hole doped cuprate
superconductors- (1) the pseudogap in the quasiparticle energy spectrum and (2)
the T-linear resistivity at high temperatures. This T-linear behavior over an
extended temperature range can be attributed to a quantum criticality,
affecting the electronic phase diagram of cuprates. Experimental in-plane and
out-of-plane resistivities of double layer Y(Ca)123 have been analyzed using
the proposed model. This phenomenological model describes the temperature and
hole content dependent resistivity over a wide range of temperature and hole
content. | 1509.01107v2 |
2015-10-12 | The Mott-Ioffe-Regel limit and resistivity crossover in a tractable electron-phonon model | Many metals display resistivity saturation - a substantial decrease in the
slope of the resistivity as a function of temperature, that occurs when the
electron scattering rate $\tau^{-1}$ becomes comparable to the Fermi energy
$E_F/\hbar$ (the Mott-Ioffe-Regel limit). At such temperatures, the usual
description of a metal in terms of ballistically propagating quasiparticles is
no longer valid. We present a tractable model of a large $N$ number of
electronic bands coupled to $N^2$ optical phonon modes, which displays a
crossover behavior in the resistivity at temperatures where $\tau^{-1}\sim
E_F/\hbar$. At low temperatures, the resistivity obeys the familiar linear
form, while at high temperatures, the resistivity still increases linearly, but
with a modified slope (that can be either lower or higher than the
low-temperature slope, depending on the band structure). The high temperature
non-Boltzmann regime is interpreted by considering the diffusion constant and
the compressibility, both of which scale as the inverse square root of the
temperature. | 1512.00041v2 |
2022-02-13 | Information Density in Multi-Layer Resistive Memories | Resistive memories store information in a crossbar arrangement of
two-terminal devices that can be programmed to patterns of high or low
resistance. While extremely compact, this technology suffers from the
"sneak-path" problem: certain information patterns cannot be recovered, as
multiple low resistances in parallel make a high resistance indistinguishable
from a low resistance. In this paper, a multi-layer device is considered, and
the number of bits it can store is derived exactly and asymptotic bounds are
developed. The information density of a series of isolated arrays with extreme
aspect ratios is derived in the single- and multi-layer cases with and without
peripheral selection circuitry. This density is shown to be non-zero in the
limit, unlike that of the arrays with moderate aspect ratios previously
considered. A simple encoding scheme that achieves capacity asymptotically is
presented. | 2202.06367v1 |
2023-09-27 | Fractal-like star-mesh transformations using graphene quantum Hall arrays | A mathematical approach is adopted for optimizing the number of total device
elements required for obtaining high effective quantized resistances in
graphene-based quantum Hall array devices. This work explores an analytical
extension to the use of star-mesh transformations such that fractal-like, or
recursive, device designs can yield high enough resistances (like 1 E{\Omega},
arguably the highest resistance with meaningful applicability) while still
being feasible to build with modern fabrication techniques. Epitaxial graphene
elements are tested, whose quantized Hall resistance at the nu=2 plateau (R_H =
12906.4 {\Omega}) becomes the building block for larger effective, quantized
resistances. It is demonstrated that, mathematically, one would not need more
than 200 elements to achieve the highest pertinent resistances | 2309.15813v1 |
1999-01-25 | Charge Transport in Synthetic Metals | The phenomenology of charge transport in synthetic metals is reviewed. It is
argued that the conventional quasiparticle picture and Boltzmann transport
theory do not apply to these materials. The central ideas of Fermi liquid
theory are reviewed, and the significant corrections produced by quasiparticle
scattering from ferromagnetic spin fluctuations in liquid $^3$He are described.
It is shown that Sr$_2$RuO$_4$ does not display the symptoms of a
nearly-ferromagnetic Fermi liquid, so the source of its odd angular momentum
pairing remains to be understood. The solution of an assisted-tunneling model
of charge transport in quasi-one dimensional materials is described. This model
has a quantum critical point and gives a resistivity that is linear in
temperature or frequency, whichever is greater. | 9901270v1 |
2000-01-11 | Interpretation of a microwave induced current step in a single intrinsic Josephson junction on a Bi-2223 thin film | Thin stacks consisting of a single intrinsic Josephson junction on
(Bi,Pb)-Sr-Ca-Cu-O thin films are investigated under the influence of external
microwave fields. The $I$-$V$-characteristic shows a single resistive branch, a
clear superconducting gap edge structure and a pronounced current step in
external microwave fields. With increasing irradiation power it shifts to
higher voltages, while the height of the step remains practically unchanged. In
a numerical simulation including an ac-magnetic field parallel to the
superconducting layers the experimental features of the structure can be
explained by a collective motion of Josephson fluxons. | 0001152v2 |
2000-12-07 | Superconductivity on the threshold of magnetism in CePd2Si2 and CeIn3 | The magnetic ordering temperature of some rare earth based heavy fermion
compounds is strongly pressure-dependent and can be completely suppressed at a
critical pressure, p$_c$, making way for novel correlated electron states close
to this quantum critical point. We have studied the clean heavy fermion
antiferromagnets CePd$_2$Si$_2$ and CeIn$_3$ in a series of resistivity
measurements at high pressures up to 3.2 GPa and down to temperatures in the mK
region. In both materials, superconductivity appears in a small window of a few
tenths of a GPa on either side of p$_c$. We present detailed measurements of
the superconducting and magnetic temperature-pressure phase diagram, which
indicate that superconductivity in these materials is enhanced, rather than
suppressed, by the closeness to magnetic order. | 0012118v1 |
2002-02-03 | Giant change in IR light transmission in La_{0.67}Ca_{0.33}MnO_{3} film near the Curie temperature: promising application in optical devices | Transport, magnetic, magneto-optical (Kerr effect) and optical (light
absorption) properties have been studied in an oriented polycrystalline
La_{0.67}Ca_{0.33}MnO_{3} film which shows colossal magneto-resistance. The
correlations between these properties are presented. A giant change in IR light
transmission (more than a 1000-fold decrease) is observed on crossing the Curie
temperature (about 270 K) from high to low temperature. Large changes in
transmittance in a magnetic field were observed as well. The giant changes in
transmittance and the large magneto-transmittance can be used for development
of IR optoelectronic devices controlled by thermal and magnetic fields.
Required material characteristics of doped manganites for these devices are
discussed. | 0202041v1 |
2002-07-10 | Crystal growth and characterization of MgB2: Relation between structure and superconducting properties | We discuss the important aspects of synthesis and crystal growth of MgB2
under high pressure (P) and temperature (T) in Mg-B-N system, including the
optimisation of P-T conditions for reproducible crystal growth, the role of
liquid phases in this process, the temperature dependence of crystal size and
the effect of growing instabilities on single crystals morphology. Extensive
experiments have been carried out on single crystals with slightly different
lattice constants and defects concentration, which revealed and possible
effects of Mg-deficiency and lattice strain on the superconducting properties
of MgB2 (Tc, Jc, residual resistivity ratio, anisotropy etc.). | 0207247v1 |
2002-07-10 | Synthesis effects on the magnetic and superconducting properties of RuSr2GdCu2O8 | A systematic study on the synthesis of the Ru-1212 compound by preparing a
series of samples that were annealed at increasing temperatures and then
quenched has been performed. It results that the optimal temperature for the
annealing lies around 1060-1065 C; a further temperature increase worsens the
phase formation. Structural order is very important and the subsequent grinding
and annealing improves it. Even if from the structural point of view the
samples appear substantially similar, the physical characterization highlight
great differences both in the electrical and magnetic properties related to
intrinsic properties of the phase as well as to the connection between the
grains as inferred from the resistive and the Curie Weiss behaviour at high
temperature as well as in the visibility of ZFC anf FC magnetic signals. | 0207265v1 |
2002-08-02 | Transport spin polarisation in SrRuO3 measured through Point Contact Andreev reflection | We report a study in which Andreev reflection using a Nb point contact is
used to measure the transport spin polarisation of the 4d itinerant ferromagnet
SrRuO3. By performing the study in high quality thin films with residual
resistivities less than 7micro-ohm-cm, we ensure that the study is done in the
ballistic limit, a regime which is difficult to reach in oxide ferromagnets.
The degree of transport spin polarisation that we find is comparable to that of
the hole doped rare-earth manganites. We conclude that the large transport spin
polarisation results mainly from a difference in the Fermi velocities between
the majority and minority spin channels in this material. | 0208044v3 |
2002-08-23 | Superconductivity in molecular solids with Jahn-Teller phonons | We analyze fulleride superconductivity at experimental doping levels,
treating the electron-electron and electron-phonon interactions on an equal
footing, and establish the existence of novel physics which helps explain the
unusually high superconducting transition temperatures in these systems. The
Jahn-Teller phonons create a local (intramolecular) pairing that is
surprisingly resistant to the Coulomb repulsion, despite the weakness of
retardation in these low-bandwidth systems. The requirement for coherence
throughout the solid to establish superconductivity then yields a very strong
doping dependence to Tc, one consistent with experiment and much stronger than
expected from standard Eliashberg theory. | 0208454v1 |
2003-08-13 | Physical properties of single-crystalline fibers of the colossal-magnetoresistance manganite La0.7Ca0.3MnO3 | We have grown high-quality single crystals of the colossal-magnetoresistance
(CMR) material La0.7Ca0.3MnO3 by using the laser heated pedestal growth (LHPG)
method. Samples were grown as fibers of different diameters, and with lengths
of the order of centimeters. Their composition and structure were verified
through X-ray diffraction, scanning electron microcopy with EDX (Energy
Dispersive X-ray Analysis) and by Rietveld analysis. The quality of the
crystalline fibers was confirmed by Laue and EBSD (Electron Backscatter
Diffraction) patterns. Rocking curves performed along the fiber axis revealed a
half-height width of 0.073 degrees. The CMR behavior was confirmed by
electrical resistivity and magnetization measurements as a function of
temperature. | 0308245v1 |
2004-07-22 | Real Space Imaging of the Microscopic Origins of the Ultrahigh Dielectric Constant in Polycrystalline CaCu3Ti4O12 | The origins of an ultrahigh dielectric constant in polycrystalline
CaCu3Ti4O12 (CCTO) was studied using the combination of impedance spectroscopy,
electron microscopy, and scanning probe microscopy (SPM). Impedance spectra
indicate that the transport properties in the 0.1 Hz .. 1 MHz frequency range
are dominated by a single parallel resistive-capacitive (RC) element with a
characteristic relaxation frequency of 16 Hz. Dc potential distributions
measurements by SPM illustrate that significant potential drops occur at the
grain boundaries, which thus can be unambiguously identified as the dominant RC
element. High frequency ac amplitude and phase distributions illustrate very
weak contrast at the interfaces, which is indicative of strong capacitive
coupling. These results demonstrate that the ultrahigh dielectric constant
reported for polycrystalline CCTO materials are related to the grain boundary
behavior. | 0407608v1 |
2004-07-28 | Room temperature tunneling magnetoresistance in magnetite based junctions: Influence of tunneling barrier | Magnetite (Fe3O4) based tunnel junctions with turret/mesa structure have been
investigated for different barrier materials (SrTiO3, NdGaO3, MgO, SiO2, and
Al2O(3-x)). Junctions with a Ni counter electrode and an aluminium oxide
barrier showed reproducibly a tunneling magnetoresistance (TMR) effect at room
temperature of up to 5% with almost ideal switching behavior. This number only
partially reflects the intrinsic high spin polarization of Fe3O4. It is
considerably decreased due to an additional series resistance within the
junction. Only SiO2 and Al2O(3-x) barriers provide magnetically decoupled
electrodes as necessary for sharp switching. The observed decrease of the TMR
effect as a function of increasing temperature is due to a decrease in spin
polarization and an increase in spin-scattering in the barrier. Among the oxide
half-metals magnetite has the potential to enhance the performance of TMR based
devices. | 0407725v1 |
2005-05-04 | Tunable charge carriers and thermoelectricity of single-crystal Ba8Ga16Sn30 | We have grown single crystals of the type-VIII intermetallic clathrate
Ba8Ga16Sn30 from both Sn and Ga flux, evaluated their compositions through
electron microprobe analysis and studied their transport properties through
measurements on temperature dependent resistivity, thermopower and Hall
coefficient. Crystals grown in Sn flux show n-type carriers and those from Ga
flux show p-type carriers, whereas all measured compositions remain very close
to the stoichiometric 8:16:30 proportion of Ba:Ga:Sn, expected from
charge-balance principles. Our results indicate a very high sensitivity of the
charge carrier nature and density with respect to the growth conditions,
leading to relevant differences in transport properties which point to the
importance of tuning this material for optimal thermoelectric performance. | 0505095v2 |
2005-05-14 | Surface morphology, structure and transport property of NaxCoO2 thin films grown by pulsed laser deposition | In this paper, we report the growth of NaxCoO2 thin films by pulsed-laser
deposition (PLD). It is shown that the concentration of sodium is very
sensitive to the substrate temperature and the target-substrate distance due to
the evaporation of sodium during the deposition. alpha prime-phase Na0.75CoO2
and gamma- phase Na0.71CoO2 thin films can be obtained with different
conditions. Correspondingly, the surface morphology of the films changes from
flake-like to particle-like. The temperature dependence of resistivity for the
films prepared with the optimal condition shows metallic behavior, consistent
with the data of NaxCoO2 single crystals. This work demonstrates that PLD is a
promising technique to get high quality NaxCoO2 thin films. | 0505360v1 |
2005-10-19 | Oxygen Isotope Effect on the Spin State Transition in (Pr$_{0.7}$Sm$_{0.3}$)$_{0.7}$Ca$_{0.3}$CoO${_3}$ | Oxygen isotope substitution is performed in the perovskite cobalt oxide
(Pr$_{0.7}$Sm$_{0.3}$)$_{0.7}$Ca$_{0.3}$CoO${_3}$ which shows a sharp spin
state transition from the intermediate spin (IS) state to the low spin (LS)
state at a certain temperature. The transition temperature of the spin state
up-shifts with the substitution of $^{16}O$ by $^{18}$O from the resistivity
and magnetic susceptibility measurements. The up-shift value is 6.8 K and an
oxygen isotope exponent ($\alpha_S$) is about -0.8. The large oxygen isotope
effect indicates strong electron-phonon coupling in this material. The
substitution of $^{16}$O by $^{18}$O leads to a decrease in the frequency of
phonon and an increase in the effective mass of electron ($m$$^\ast$), so that
the bandwidth W is decreased and the energy difference between the different
spin states is increased. This is the reason why the $T_s$ is shifted to high
temperature with oxygen isotopic exchange. | 0510499v1 |
2005-10-24 | Combining half-metals and multiferroics into epitaxial heterostructures for spintronics | We report on the growth of epitaxial bilayers of the La2/3Sr1/3MnO3 (LSMO)
half-metallic ferromagnet and the BiFeO3 (BFO) multiferroic, on SrTiO3(001) by
pulsed laser deposition. The growth mode of both layers is two-dimensional,
which results in unit-cell smooth surfaces. We show that both materials keep
their properties inside the heterostructures, i.e. the LSMO layer (11 nm thick)
is ferromagnetic with a Curie temperature of ~330K, while the BFO films shows
ferroelectricity down to very low thicknesses (5 nm). Conductive-tip atomic
force microscope mappings of BFO/LSMO bilayers for different BFO thicknesses
reveal a high and homogeneous resistive state for the BFO film that can thus be
used as a ferroelectric tunnel barrier in tunnel junctions based on a
half-metal. | 0510625v1 |
2006-05-22 | Dissipative Van der Waals interaction between a small particle and a metal surface | We use a general theory of the fluctuating electromagnetic field to calculate
the friction force acting on a small neutral particle, e.g., a physisorbed
molecule, or a nanoscale object with arbitrary dispersive and absorptive
dielectric properties, moving near a metal surface. We consider the dependence
of the electromagnetic friction on the temperature $T$, the separation $d$, and
discuss the role of screening, non-local and retardation effects. We find that
for high resistivity materials, the dissipative van der Waals interaction can
be an important mechanism of vibrational energy relaxation of physisorbed
molecules, and friction for microscopic solids. Several controversial topics
related to electromagnetic dissipative shear stress is considered. The problem
of local heating of the surface by an STM tip is also briefly commented on. | 0605525v1 |
1999-04-15 | Comparative Energy Dependence of Proton and Pion Degradation in Diamond | A comparative theoretical study of the damages produced by protons and pions,
in the energy range 50 MeV - 50 GeV, in diamond, is presented. The
concentration of primary defects (CPD) induced by hadron irradiation is used to
describe material degradation. The CPD has very different behaviours for
protons and pions: the proton degradation is important at low energies and is
higher than the pion one in the whole energy range investigated, with the
exception of the Delta33 resonance region, where a large maximum of the
degradation exists for pions. In comparison with silicon, the most investigated
and the most studied material for detectors, diamond theoretically proves to be
one order of magnitude more resistant, both to proton and pion irradiation. | 9904342v1 |
2008-10-06 | Theory of the spontaneous buckling of doped graphene | Graphene is a realization of an esoteric class of materials -- electronic
crystalline membranes. We study the interplay between the free electrons and
the two-dimensional crystal, and find that it induces a substantial effect on
the elastic structure of the membrane. For the hole-doped membrane, in
particular, we predict a spontaneous buckling. In addition, attenuation of
elastic waves is expected, due to the effect of corrugations on the bulk
modulus. These discoveries have a considerable magnitude in graphene, affecting
both its mesoscopic structure, and its electrical resistivity, which has an
inherent asymmetry between hole- and electron-doped graphene. | 0810.1062v4 |
2009-06-12 | Giant magnetic anisotropy changes in Sr2CrReO6 thin films on BaTiO3 | The integration of ferromagnetic and ferroelectric materials into hybrid
heterostructures yields multifunctional systems with improved or novel
functionality. We here report on the structural, electronic and magnetic
properties of the ferromagnetic double perovskite Sr2CrReO6, grown as epitaxial
thin film onto ferroelectric BaTiO3. As a function of temperature, the
crystal-structure of BaTiO3 undergoes phase transitions, which induce
qualitative changes in the magnetic anisotropy of the ferromagnet. We observe
abrupt changes in the coercive field of up to 1.2T along with resistance
changes of up to 6.5%. These results are attributed to the high sensitivity of
the double perovskites to mechanical deformation. | 0906.2276v1 |
2010-01-22 | Conducting interfaces between band insulating oxides: the LaGaO3/SrTiO3 | We show that the growth of the heterostructure LaGaO3/SrTiO3 yields the
formation of a highly conductive interface. Our samples were carefully analyzed
by high resolution electron microscopy, in order to assess their crystal
perfection and to evaluate the abruptness of the interface. Their carrier
density and sheet resistance are compared to the case of LaAlO3/SrTiO3 and a
superconducting transition is found. The results open the route to widening the
field of polar-non polar interfaces, pose some phenomenological constrains to
their underlying physics and highlight the chance of tailoring their properties
for future applications by adopting suitable polar materials. | 1001.3956v2 |
2010-06-15 | Fluorographene: Two Dimensional Counterpart of Teflon | We report a stoichiometric derivative of graphene with a fluorine atom
attached to each carbon. Raman, optical, structural, micromechanical and
transport studies show that the material is qualitatively different from the
known graphene-based nonstoichiometric derivatives. Fluorographene is a
high-quality insulator (resistivity >10^12 Ohm per square) with an optical gap
of 3 eV. It inherits the mechanical strength of graphene, exhibiting Young's
modulus of 100 N/m and sustaining strains of 15%. Fluorographene is inert and
stable up to 400C even in air, similar to Teflon. | 1006.3016v2 |
2010-10-26 | Graphene to Graphane: Novel Electrochemical Conversion | A novel electrochemical means to generate atomic hydrogen, simplifying the
synthesis and controllability of graphane formation on graphene is presented.
High quality, vacuum grown epitaxial graphene (EG) was used as starting
material for graphane conversion. A home-built electrochemical cell with Pt
wire and exposed graphene as the anode and cathode, respectively, was used to
attract H+ ions to react with the exposed graphene. Cyclic voltammetry of the
cell revealed the potential of the conversion reaction as well as oxidation and
reduction peaks, suggesting the possibility of electrochemically reversible
hydrogenation. A sharp increase in D peak in the Raman spectra of EG, increase
of D/G ratio, introduction of a peak at ~2930 cm-1 and respective peak shifts
as well as a sharp increase in resistance showed the successful hydrogenation
of EG. This conversion was distinguished from lattice damage by thermal
reversal back to graphene at 1000{\deg}C. | 1010.5458v1 |
2010-11-15 | Transfer Printing Approach to All-Carbon Nanoelectronics | Transfer printing methods are used to pattern and assemble monolithic carbon
nanotube (CNT) thin-film transistors on large-area transparent, flexible
substrates. Airbrushed CNT thin-films with sheet resistance 1kOhmsquare^{-1} at
80% transparency were used as electrodes, and high quality chemical vapor
deposition (CVD)-grown CNT networks were used as the semiconductor component.
Transfer printing was used to pre-pattern and assemble thin film transistors on
polyethylene terephthalate (PET) substrates which incorporated
Al_{2}O_{3}/poly-methylmethacrylate (PMMA) dielectric bi-layer. CNT-based
ambipolar devices exhibit field-effect mobility in range 1 - 33 cm^{2}/Vs and
on/off ratio ~10^{3}, comparable to the control devices fabricated using Au as
the electrode material. | 1011.3269v1 |
2011-07-05 | Hidden spin liquid in an antiferromagnet: Applications to FeCrAs | The recently studied material FeCrAs exhibits a surprising combination of
experimental signatures, with metallic, Fermi liquid like specific heat but
resistivity showing strong non-metallic character. The Cr sublattice posseses
local magnetic moments, in the form of stacked (distorted) Kagome lattices.
Despite the high degree of magnetic frustration, anti-ferromagnetic order
develops below ~125K suggesting the non-magnetic Fe sublattice may play a role
in stabilizing the ordering. From the material properties we propose a
microscopic Hamiltonian for the low energy degrees of freedom, including the
non-magnetic Fe sublattice, and study its properties using slave-rotor mean
field theory. Using this approach we find a spin liquid phase on the Fe
sublattice, which survives even in the presence of the magnetic Cr sublattice.
Finally, we suggest that the features of FeCrAs can be qualitatively explained
by critical fluctuations in the non-magnetic sublattice Fe due to proximity to
a metal-insulator transition. | 1107.1002v1 |
2011-11-16 | Infrared Spectroscopy of Wafer-Scale Graphene | We report on spectroscopy results from the mid- to far-infrared on
wafer-scale graphene, grown either epitaxially on silicon carbide, or by
chemical vapor deposition. The free carrier absorption (Drude peak) is
simultaneously obtained with the universal optical conductivity (due to
interband transitions), and the wavelength at which Pauli blocking occurs due
to band filling. From these the graphene layer number, doping level, sheet
resistivity, carrier mobility, and scattering rate can be inferred. The mid-IR
absorption of epitaxial two-layer graphene shows a less pronounced peak at
0.37\pm0.02 eV compared to that in exfoliated bilayer graphene. In heavily
chemically-doped single layer graphene, a record high transmission reduction
due to free carriers approaching 40% at 250 \mum (40 cm-1) is measured in this
atomically thin material, supporting the great potential of graphene in
far-infrared and terahertz optoelectronics. | 1111.3714v1 |
2011-12-22 | Single crystal growth of YbRh2Si2 and YbIr2Si2 | We report on the single crystal growth of the heavy-fermion compounds
YbRh2Si2 and YbIr2Si2 using a high-temperature indium-flux technique. The
optimization of the initial composition and the temperature-time profile lead
to large (up to 100 mg) and clean (\rho_0=0.5 \mu\Omega cm) single crystals of
YbRh2Si2. Low-temperature resistivity measurements revealed a sample dependent
temperature exponent below 10 K, which for the samples with highest quality
deviates from a linear-in-T behaviour. Furthermore, we grew single crystals of
the alloy series Yb(Rh_(1-x)Ir_x)2Si2 with 0<x<0.23 and report the structural
details. For pure YbIr2Si2, we establish the formation of two crystallographic
modifications, where the magnetic 4f-electrons have different physical ground
states. | 1112.5251v1 |
2012-02-11 | Observation of Andreev bound state and multiple energy gaps in the non-centrosymmetric superconductor BiPd | We report directional point contact Andreev reflection (PCAR) measurements on
high-quality single crystals of the non-centrosymmetric superconductor, BiPd.
The PCAR spectra measured on different crystallographic faces of the single
crystal clearly show the presence of multiple superconducting energy gaps. For
point contacts with low resistance, in addition to the superconducting gap
feature, a pronounced zero bias conductance peak is observed. These
observations provide strong evidence of the presence of unconventional order
parameter in this material. | 1202.2454v2 |
2012-08-09 | Frictional characteristics of exfoliated and epitaxial graphene | To determine the friction coefficient of graphene, micro-scale scratch tests
are conducted on exfoliated and epitaxial graphene at ambient conditions. The
experimental results show that the monolayer, bilayer, and trilayer graphene
all yield friction coefficients of approximately 0.03. The friction coefficient
of pristine graphene is less than that of disordered graphene, which is treated
by oxygen plasma. Ramping force scratch tests are performed on graphene with
various numbers of layers to determine the normal load required for the probe
to penetrate graphene. A very low friction coefficient and also its high
pressure resistance make graphene a promising material for antiwear coatings. | 1208.1830v1 |
2012-10-05 | A study of gas contaminants and interaction with materials in RPC closed loop systems | Resistive Plate Counters (RPC) detectors at the Large Hadron Collider (LHC)
experiments use gas recirculation systems to cope with large gas mixture
volumes and costs. In this paper a long-term systematic study about gas
purifiers, gas contaminants and detector performance is discussed. The study
aims at measuring the lifetime of purifiers with unused and used cartridge
material along with contaminants release in the gas system. During the
data-taking the response of several RPC double-gap detectors was monitored in
order to characterize the correlation between dark currents, filter status and
gas contaminants. | 1210.1819v1 |
2013-01-22 | Thermoelectric Properties of Intermetallic Semiconducting RuIn3 and Metallic IrIn3 | Low temperature (<400 K) thermoelectric properties of semiconducting RuIn3
and metallic IrIn3 are reported. RuIn3 is a narrow band gap semiconductor with
a large n-type Seebeck coefficient at room temperature (S(290K)~400 {\mu}V/K),
but the thermoelectric Figure of merit (ZT(290K) = 0.007) is small because of
high electrical resistivity and thermal conductivity ({\kappa}(290 K) ~ 2.0 W/m
K). IrIn3 is a metal with low thermopower at room temperature (S(290K)~20
{\mu}V/K) . Iridium substitution on the ruthenium site has a dramatic effect on
transport properties, which leads to a large improvement in the power factor
and corresponding Figure of merit (ZT(380 K) = 0.053), improving the efficiency
of the material by an over of magnitude. | 1301.5353v1 |
2013-02-21 | Study of gas contaminants and interaction with materials in RPC closed loop system | Resistive Plate Counters (RPC) detectors at the Large Hadron Collider (LHC)
experiments use gas recirculation systems to cope with large gas mixture
volumes and costs. In this paper a long-term systematic study about gas
purifiers, gas contaminants and detector performance is discussed. The study
aims at measuring the lifetime of purifiers with new and used cartridge
material along with contaminants release in the gas system. During the
data-taking the response of several RPC double-gap detectors was monitored in
order to characterize the correlation between dark currents, filter status and
gas contaminants. | 1302.5225v2 |
2013-04-24 | High sensitivity measurements of thermal properties of textile fabrics | A new testing apparatus is proposed to measure the thermal properties of
fabrics made from polymeric materials. The calibration of the apparatus and the
data acquisition procedure are considered in detail in order to measure thermal
conductivity, resistance, absorption and diffusivity constants of the tested
fabric samples. Differences between dry and wet fabrics have been carefully
detected and analyzed. We have developed a new measurement protocol, the
"ThermoTex" protocol, which agrees with the UNI EN 31092 standard and entails
an accurate quantification of the experimental errors according to a standard
statistical analysis, thus allowing a rigorous investigation of the physical
behavior of the phenomena involved. As a consequence, our machinery exhibits
great potentialities for optimizing the thermal comfort of fabrics, according
to the market demand, thanks to the possible development of a predictive
phenomenological theory of the effects involved. | 1304.6714v1 |
2013-07-12 | High-energy radiation damage in zirconia: modeling results | Zirconia is viewed as a material of exceptional resistance to amorphization
by radiation damage, and consequently proposed as a candidate to immobilize
nuclear waste and serve as an inert nuclear fuel matrix. Here, we perform
molecular dynamics simulations of radiation damage in zirconia in the range of
0.1-0.5 MeV energies with full account of electronic energy losses. We find
that the lack of amorphizability co-exists with a large number of point defects
and their clusters. These, importantly, are largely isolated from each other
and therefore represent a dilute damage that does not result in the loss of
long-range structural coherence and amorphization. We document the nature of
these defects in detail, including their sizes, distribution and morphology,
and discuss practical implications of using zirconia in intense radiation
environments. | 1307.3380v4 |
2013-08-16 | Quantum Criticality in Electron-doped BaFe_{2-x}Ni_xAs_2 | A quantum critical point (QCP) is a point in a system's phase diagram at
which an order is completely suppressed at absolute zero temperature (T). The
presence of a quantum critical point manifests itself in the finite-T physical
properties, and often gives rise to new states of matter. Superconductivity in
the cuprates and in heavy fermion materials is believed by many to be mediated
by fluctuations associated with a quantum critical point. In the
recently-discovered iron-pnictide high temperature superconductors, it is
unknown whether a QCP exists or not in a carrier-doped system. Here we report
transport and nuclear magnetic resonance (NMR) measurements on
BaFe_{2-x}Ni_xAs_2 (0 =< x =< 0.17). We find two critical points at x_{c1} =
0.10 and x_{c2} = 0.14. The electrical resistivity follows \rho = \rho_0 +
A*T^n, with n = 1 around x_{c1} and another minimal n = 1.1 at x_{c2}. By NMR
measurements, we identity x_{c1} to be a magnetic QCP and suggest that x_{c2}
is a new type of QCP associated with a nematic structural phase transition. Our
results suggest that the superconductivity in carrier-doped pnictides is
closely linked to the quantum criticality. | 1308.3539v1 |
2013-11-07 | Helium Ion Microscopy | Helium Ion Microcopy (HIM) based on Gas Field Ion Sources (GFIS) represents a
new ultra high resolution microscopy and nano-fabrication technique. It is an
enabling technology that not only provides imagery of conducting as well as
uncoated insulating nano-structures but also allows to create these features.
The latter can be achieved using resists or material removal due to sputtering.
The close to free-form sculpting of structures over several length scales has
been made possible by the extension of the method to other gases such as Neon.
A brief introduction of the underlying physics as well as a broad review of the
applicability of the method is presented in this review. | 1311.1711v2 |
2014-04-08 | Fingerprints of Inelastic Transport at the Surface of the Topological Insulator Bi2Se3: Role of Electron-Phonon Coupling | We report on electric-field and temperature dependent transport measurements
in exfoliated thin crystals of Bi$_{2}$Se$_{3}$ topological insulator. At low
temperatures ($< 50$ K) and when the chemical potential lies inside the bulk
gap, the crystal resistivity is strongly temperature dependent, reflecting
inelastic scattering due to the thermal activation of optical phonons. A linear
increase of the current with voltage is obtained up to a threshold value at
which current saturation takes place. We show that the activated behavior, the
voltage threshold and the saturation current can all be quantitatively
explained by considering a single optical phonon mode with energy $\hbar \Omega
\approx 8$ meV. This phonon mode strongly interacts with the surface states of
the material and represents the dominant source of scattering at the surface at
high electric fields. | 1404.2198v1 |
2014-09-03 | Significant reduction of lattice thermal conductivity by electron-phonon interaction in silicon with high carrier concentrations: a first-principles study | Electron-phonon interaction has been well known to create major resistance to
electron transport in metals and semiconductors, whereas less studies were
directed to its effect on the phonon transport, especially in semiconductors.
We calculate the phonon lifetimes due to scattering with electrons (or holes),
combine them with the intrinsic lifetimes due to the anharmonic phonon-phonon
interaction, all from first-principles, and evaluate the effect of the
electron-phonon interaction on the lattice thermal conductivity of silicon.
Unexpectedly, we find a significant reduction of the lattice thermal
conductivity at room temperature as the carrier concentration goes above 1e19
cm-3 (the reduction reaches up to 45% in p-type silicon at around 1e21 cm-3), a
range of great technological relevance to thermoelectric materials. | 1409.1268v1 |
2015-01-16 | Hyperdoping silicon with selenium: solid vs. liquid phase epitaxy | Chalcogen-hyperdoped silicon shows potential applications in silicon-based
infrared photodetectors and intermediate band solar cells. Due to the low solid
solubility limits of chalcogen elements in silicon, these materials were
previously realized by femtosecond or nanosecond laser annealing of implanted
silicon or bare silicon in certain background gases. The high energy density
deposited on the silicon surface leads to a liquid phase and the fast
recrystallization velocity allows trapping of chalcogen into the silicon
matrix. However, this method encounters the problem of surface segregation. In
this paper, we propose a solid phase processing by flash-lamp annealing in the
millisecond range, which is in between the conventional rapid thermal annealing
and pulsed laser annealing. Flash lamp annealed selenium-implanted silicon
shows a substitutional fraction of around 70% with an implanted concentration
up to 2.3%. The resistivity is lower and the carrier mobility is higher than
those of nanosecond pulsed laser annealed samples. Our results show that
flash-lamp annealing is superior to laser annealing in preventing surface
segregation and in allowing scalability. | 1501.03953v1 |
2015-03-20 | Strong charge ordering above room temperature in B-site disordered electron-doped manganite SrMn0.875Mo0.125O3-δ | Low as well as high-temperature electron and x-ray diffraction studies have
been carried out on a rare-earth free B-site disordered electron-doped
manganite SrMn0.875.Mo0.125O3-{\delta} in the temperature range of 83K to 637K.
These studies reveal the occurrence of strong charge ordering (CO) at room
temperature in a pseudo tetragonally distorted perovskite phase with
space-group Pmmm. Non integral modulation vector of 8.95 times along [-110]
indicates a charge density wave type modulation. The CO phase with basic
perovskite structure Pmmm transforms to a charge disorder cubic phase through a
first order phase transition at 355K. Supporting temperature dependent
measurements of resistance and magnetization show a metal-insulator and
antiferromagnetic transitions across 355K with a wide hysterisis ranging from
150K to 365K. The occurrence of pseudo tetragonality of the basic perovskite
lattice with c/a < 1 together with charge-ordered regions with 2-dimensional
modulation have been analyzed as the coexistence of two CO phases with
3dx2/3dy2 type and 3dx2-y2 type orbital ordering. | 1503.06000v1 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.