publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2020-11-20 | Large Thermoelectric Power Factor in Whisker Crystals of Solid Solutions of the One-Dimensional Tellurides Ta4SiTe4 and Nb4SiTe4 | One-dimensional tellurides Ta4SiTe4 and Nb4SiTe4 were found to show high
thermoelectric performance below room temperature. This study reported the
synthesis and thermoelectric properties of whisker crystals of
Ta4SiTe4-Nb4SiTe4 solid solutions and Mo- or Ti-doped (Ta0.5Nb0.5)4SiTe4.
Thermoelectric power of the solid solutions systematically increased with
increasing Ta content, while their electrical resistivity was unexpectedly
small. Mo- and Ti-doped (Ta0.5Nb0.5)4SiTe4 showed n- and p-type thermoelectric
properties with large power factors exceeding 40 microW cm-1 K-2, respectively.
The fact that not only Ta4SiTe4 and Nb4SiTe4 but also their solid solutions
showed high performance indicated that this system is a promising candidate for
thermoelectric applications at low temperatures. | 2011.10162v1 |
2020-12-11 | Absence of superconductivity in topological metal ScInAu$_2$ | The Heusler compound ScInAu$_2$ was previously reported to have a
superconducting ground state with a critical temperature of 3.0 K. Recent high
throughput calculations have also predicted that the material harbors a
topologically non-trivial band structure similar to that reported for
beta-PdBi$_2$. In an effort to explore the interplay between the
superconducting and topological properties properties, electrical resistance,
magnetization, and x-ray diffraction measurements were performed on
polycrystalline ScInAu$_2$. The data reveal that high-quality polycrystalline
samples lack the super-conducting transition present samples that have not been
annealed. These results indicate the earlier reported superconductivity is
non-intrinsic. Several compounds in the Au-In-Sc ternary phase space (ScAu$_2$,
ScIn$_3$, and ScInAu$_2$) were explored in an attempt to identify the secondary
phase responsible for the non-intrinsic superconductivity. The results suggest
that elemental In is responsible for the reported superconductivity in
ScInAu$_2$. | 2012.06501v1 |
2021-02-24 | Synthesis of new high-entropy alloy-type Nb3 (Al, Sn, Ge, Ga, Si) superconductors | Studies on high-entropy alloy (HEA) superconductors have recently been
increasing, particularly in the fields of materials science and condensed
matter physics. To contribute to research on new HEA-type superconductors, in
our study we synthesized polycrystalline samples of A15-type superconductors of
Nb3Al0.2Sn0.2Ge0.2Ga0.2Si0.2 (#1) and Nb3Al0.3Sn0.3Ge0.2Ga0.1Si0.1 (#2) with an
HEA-type site by arc melting. Elemental and structural analyses revealed that
the compositions of the obtained samples satisfied the HEA state criteria.
Superconducting transitions were observed at 9.0 and 11.0 K for #1 and #2,
respectively, in the temperature dependence of magnetization and electrical
resistivity. Specific heat measurements revealed that the Sommerfeld
coefficient, Debye temperature, and {\Delta}C/{\gamma}Tc for the obtained
samples were close to those reported for conventional Nb3Sn family
superconductors. | 2102.12271v1 |
2021-02-24 | Spin waves and high-frequency response in layered superconductors with helical magnetic structure | We evaluate the spin-wave spectrum and dynamic susceptibility in a layered
superconductors with helical interlayer magnetic structure. We especially focus
on the structure in which the moments rotate 90$^{\circ}$ from layer to layer
realized in the iron pnictide RbEuFe$_{4}$As$_{4}$. The spin-wave spectrum in
superconductors is strongly renormalized due to the long-range electromagnetic
interactions between the oscillating magnetic moments. This leads to strong
enhancement of the frequency of the mode coupled with uniform field and this
enhancement exists only within a narrow range of the c-axis wave vectors of the
order of the inverse London penetration depth. The key feature of materials
like RbEuFe$_{4}$As$_{4}$ is that this uniform mode corresponds to the maximum
frequency of the spin-wave spectrum with respect to c-axis wave vector. As a
consequence, the high-frequency surface resistance acquires a very distinct
asymmetric feature spreading between the bare and renormalized frequencies. We
also consider excitation of spin waves with Josephson effect in a tunneling
contact between helical-magnetic and conventional superconductors and study the
interplay between the spin-wave features and geometrical cavity resonances in
the current-voltage characteristics. | 2102.12445v2 |
2021-06-08 | High electrical conduction of Sb square net in anti-ThCr$_2$Si$_2$ type La$_2$O$_2$Sb thin film grown by multilayer solid-phase epitaxy | Anti-ThCr$_2$Si$_2$ type $RE_2$O$_2$Sb ($RE$ = rare earth) with Sb square net
has shown insulating conduction so far. Here we report the synthesis of
La$_2$O$_2$Sb epitaxial thin films for the first time by multilayer solid-phase
epitaxy. The valence state of Sb was about -2 evaluated from X-ray
photoemission spectroscopy measurement, and the indirect band gap of 0.17 eV
was observed. The La$_2$O$_2$Sb epitaxial thin film showed unexpectedly high
electrical conduction as a narrow gap semiconductor, whose resistivity at room
temperature was approximately ten-thousand-fold lower than that of
La$_2$O$_2$Sb bulk polycrystal, attributed to increased carrier mobility
probably due to suppressed Sb dimerization. | 2106.04713v1 |
2021-07-12 | Hysteretic effects and magnetotransport of electrically switched CuMnAs | Antiferromagnetic spintronics allows us to explore storing and processing
information in magnetic crystals with vanishing magnetization. In this
manuscript, we investigate magnetoresistance effects in antiferromagnetic
CuMnAs upon switching into high-resistive states using electrical pulses. By
employing magnetic field sweeps up to 14 T and magnetic field pulses up to
$\sim$ 60 T, we reveal hysteretic phenomena and changes in the
magnetoresistance, as well as the resilience of the switching signal in CuMnAs
to the high magnetic field. These properties of the switched state are
discussed in the context of recent studies of antiferromagnetic textures in
CuMnAs. | 2107.05724v1 |
2021-08-20 | Quantum oscillations in an optically-illuminated two-dimensional electron system at the LaAlO$_3$/SrTiO$_3$ interface | We have investigated the illumination effect on the magnetotransport
properties of a two-dimensional electron system at the LaAlO$_3$/SrTiO$_3$
interface. The illumination significantly reduces the zero-field sheet
resistance, eliminates the Kondo effect at low-temperature, and switches the
negative magnetoresistance into the positive one. A large increase in the
density of high-mobility carriers after illumination leads to quantum
oscillations in the magnetoresistance originating from the Landau quantization.
The carrier density ($\sim 2 \times 10^{12}$ cm$^{-2}$) and effective mass
($\sim 1.7 ~m_e$) estimated from the oscillations suggest that the
high-mobility electrons occupy the d$_{xz/yz}$ subbands of Ti:t$_{2g}$ orbital
extending deep within the conducting sheet of SrTiO$_3$. Our results
demonstrate that the illumination which induces additional carriers at the
interface can pave the way to control the Kondo-like scattering and study the
quantum transport in the complex oxide heterostructures. | 2108.09156v1 |
2021-11-27 | Antiferromagnetic order in MnBi2Te4 films grown on Si(111) by molecular beam epitaxy | MnBi2Te4 has recently been predicted and shown to be a magnetic topological
insulator with intrinsic antiferromagnetic order. However, it remains a
challenge to grow stoichiometric MnBi2Te4 films by molecular beam epitaxy (MBE)
and to observe pure antiferromagnetic order by magnetometry. We report on a
detailed study of MnBi2Te4 films grown on Si(111) by MBE with elemental
sources. Films of about 100 nm thickness are analyzed in stoichiometric,
structural, magnetic and magnetotransport properties with high accuracy.
High-quality MnBi2Te4 films with nearly perfect septuple-layer structure are
realized and structural defects typical for epitaxial van-der-Waals layers are
analyzed. The films reveal antiferromagnetic order with a Neel temperature of
19 K, a spin-flop transition at a magnetic field of 2.5 T and a resistivity of
1.6 mOhm cm. These values are comparable to that of bulk MnBi2Te4 crystals. Our
results provide an important basis for realizing and identifying single-phase
MnBi2Te4 films with antiferromagnetic order grown by MBE. | 2111.13960v1 |
2021-12-04 | Superconducting and normal state properties of high entropy alloy Nb-Re-Hf-Zr-Tiinvestigated by muon spin relaxation and rotation | Superconducting high entropy alloy (HEA) are emerging as a new class of
superconducting materials. It provides a unique opportunity to understand the
complex interplay of disorder and superconductivity. We report the synthesis
and detail bulk and microscopic characterization of
Nb$_{60}$Re$_{10}$Zr$_{10}$Hf$_{10}$Ti$_{10}$ HEA alloy using transport,
magnetization, specific heat, and muon spin rotation/relaxation ($\mu$SR)
measurements. Bulk superconductivity with transition temperature $T_{C}$ = 5.7
K confirmed by magnetization, resistivity, and heat capacity measurements.
Zero-field $\mu$SR measurement shows that the superconducting state preserves
time-reversal symmetry, and transverse-field measurements of the superfluid
density are well described by an isotropic s-wave model. | 2112.02388v1 |
2022-01-31 | Disorder-mediated quenching of magnetization in NbVTiAl: Theory and Experiment | In this paper, we present the structural, electronic, magnetic and transport
properties of a equiatomic quaternary alloy NbVTiAl. The absence of (111) and
(200) peaks in X-ray diffraction (XRD) data confirms the A2-type structure.
Magnetization measurements indicate a high Curie temperature and a negligibly
small magnetic moment ($\sim 10^{-3} \mu_B/f.u.$) These observations are
indicative of fully compensated ferrimagnetism in the alloy.
Temperature-dependent resistivity indicates metallic nature. Ab-initio
calculation of fully ordered NbVTiAl structure confirms a nearly half metallic
behavior with a high spin polarization ($\sim$ 90 \%) and a net magnetic moment
of 0.8 $\mu_B/f.u.$ (in complete contrast to the experimental observation). One
of the main objective of the present paper is to resolve and explain the
long-standing discrepancy between theoretical prediction and experimental
observation of magnetization for V-based quaternary Heusler alloys, in general.
To gain an in-depth understanding, we modelled various disordered states and
its subsequent effect on the magnetic and electronic properties. The
discrepancy is attributed to the A2 disorder present in the system, as
confirmed by our XRD data. The presence of disorder also causes the emergence
of finite states at the Fermi level, which impacts the spin polarization of the
system. | 2201.13037v1 |
2022-03-12 | Quantum transport evidence of the boundary states and Lifshitz transition in Bi$_4$Br$_4$ | The quasi-one-dimensional van der Waals compound Bi$_4$Br$_4$ was recently
found to be a promising high-order topological insulator with exotic electronic
states. In this paper, we study the electrical transport properties of
Bi$_4$Br$_4$ bulk crystals. Two electron-type samples with different electron
concentrations are investigated. Both samples have saturation resistivity
behavior in low temperature. In the low-concentration sample, two-dimensional
quantum oscillations are clearly observed in the magnetoresistance
measurements, which are attributed to the band-bending-induced surface state on
the (001) facet. In the high-concentration sample, the angular
magnetoresistance exhibits two pairs of symmetrical sharp valleys with an
angular difference close to the angle between the crystal planes (001) and
(100). The additional valley can be explained by the contribution of the
boundary states on the (100) facet. Besides, Hall measurements at low
temperatures reveal an anomalous decrease of electron concentration with
increasing temperature, which can be explained by the temperature-induced
Lifshitz transition. These results shed light on the abundant surface and
boundary state transport signals and the temperature-induced Lifshitz
transition in Bi$_4$Br$_4$. | 2203.06529v1 |
2022-06-21 | Second harmonic AC calorimetry technique within a diamond anvil cell | Tuning the energy density of matter at high pressures gives rise to exotic
and often unprecedented properties, e.g., structural transitions,
insulator-metal transitions, valence fluctuations, topological order, and the
emergence of superconductivity. The study of specific heat has long been used
to characterize these kinds of transitions, but their application to the
diamond anvil cell (DAC) environment has proved challenging. Limited work has
been done on the measurement of specific heat within DACs, in part due to the
difficult experimental setup. To this end we have developed a novel method for
the measurement of specific heat within a DAC that is independent of the DAC
design and therefore readily compatible with any DACs already performing high
pressure resistance measurements. As a proof-of-concept, specific heat
measurements of the MgB2 superconductor were performed, showing a clear anomaly
at the transition temperature (Tc), indicative of bulk superconductivity. This
technique allows for specific heat measurements at higher pressure than
previously possible. | 2206.10072v1 |
2022-08-10 | Synthesis and Superconductivity in Yttrium-Cerium Hydrides at Moderate Pressures | Inspired by the high critical temperature in yttrium superhydride and the low
stabilized pressure in superconducting cerium superhydride, we carry out four
independent runs to synthesize yttrium-cerium alloy hydrides. The phases
examined by the Raman scattering and x-ray diffraction measurements. The
superconductivity is detected with the zero-resistance state at the critical
temperature in the range of 97-140 K at pressures ranging from 114 GPa to
120$\pm$4 GPa. The maximum critical temperature of the synthesized hydrides is
larger than those reported for cerium hydrides, while the corresponding
stabilized pressure is much lower than those for superconducting yttrium
hydrides. The structural analysis and theoretical calculations suggest that the
phase of Y$_{0.5}$Ce$_{0.5}$H$_9$ has the space group $P6_3/mmc$ with the
calculated critical temperature of 119 K, in fair agreement with the
experiments. These results indicate that alloying superhydrides indeed can
maintain relatively high critical temperature at modest pressures accessible by
many laboratories. | 2208.05191v1 |
2022-10-12 | Field Induced Multiple Superconducting Phases in UTe2 along Hard Magnetic Axis | The superconducting (SC) phase diagram in uranium ditelluride is explored
under magnetic fields ($H$) along the hard magnetic b-axis using a high-quality
single crystal with $T_{\rm c} = 2.1$ K. Simultaneous electrical resistivity
and AC magnetic susceptibility measurements discern low- and high-field SC
(LFSC and HFSC, respectively) phases with contrasting field-angular dependence.
Crystal quality increases the upper critical field of the LFSC phase, but the
$H^{\ast}$ of $\sim$15 T, at which the HFSC phase appears, is always the same
through the various crystals. A phase boundary signature is also observed
inside the LFSC phase near $H^{\ast}$, indicating an intermediate SC phase
characterized by small flux pinning forces. | 2210.05909v2 |
2022-10-20 | Nanowire bolometer using a 2D high-temperature superconductor | Superconducting nanowires are very important due to their applications
ranging from quantum technology to astronomy. In this work, we implement a
non-invasive process to fabricate nanowires of high-$T_\text{c}$ superconductor
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (BSCCO). We demonstrate that our nanowires
can be used as bolometers in the visible range with very high responsivity of
9.7 $\times$ 10$^{3}$ V/W. Interestingly, in a long (30 $\mu$m) nanowire of 9
nm thickness and 700 nm width, we observe bias current-dependent localized
spots of maximum photovoltage. Moreover, the scalability of the bolometer
responsivity with the normal state resistance of the nanowire could allow
further performance improvement by increasing the nanowire length in a meander
geometry. We observe phase slip events in nanowires with small cross-sections
(12 nm thick, 300 nm wide, and 3 $\mu$m long) at low temperatures. Our study
presents a scalable method for realizing sensitive bolometers working near the
liquid-nitrogen temperature. | 2210.11254v2 |
2023-01-16 | Role of disorder and strong 5$d$ electron correlation in the electronic structure of Sr2TiIrO6 | Transport and magnetic properties along with high resolution valence band
photoemission study of disordered double perovskite Sr$_{2}$TiIrO$_{6}$ has
been investigated. Insulator to insulator transition along with a magnetic
transition concurrently occurs at 240 K. Comparison of valence band
photoemission with band structure calculations suggests that the spin orbit
coupling as well as electron correlation are necessary to capture the line
shape and width of the Ir 5$d$ band. Room temperature valence band
photoemission spectra show negligibly small intensity at Fermi energy, $E_{F}$.
Fermi cut-off is observed at low temperatures employing high resolution. The
spectral density of states at room temperature exhibits $|E-E_{F}|^{2}$ energy
dependence signifying the role of electron-electron interaction. This energy
dependence changes to $|E-E_{F}|^{3/2}$ below the magnetic transition
evidencing the role of electron-magnon coupling in magnetically ordered state.
The evolution of pseudogap ($\pm$12 meV) explains the sudden increase in
resistivity ($\rho$) below 50 K in this disordered system. The temperature
dependent spectral density of states at $E_{F}$ exhibiting $T^{1/2}$ behaviour
verifies Altshuler-Aronov theory for correlated disordered systems. | 2301.06275v1 |
2023-01-20 | Giant resonant enhancement for photo-induced superconductivity in K$_3$C$_{60}$ | Photo-excitation at terahertz and mid-infrared frequencies has emerged as a
new way to manipulate functionalities in quantum materials, in some cases
creating non-equilibrium phases that have no equilibrium analogue. In
K$_3$C$_{60}$, a metastable zero-resistance phase was documented with optical
properties and pressure dependences compatible with non-equilibrium high
temperature superconductivity. Here, we report the discovery of a dominant
energy scale for this phenomenon, along with the demonstration of a giant
increase in photo-susceptibility near 10 THz excitation frequency. At these
drive frequencies a metastable superconducting-like phase is observed up to
room temperature for fluences as low as ~400 $\mu J/cm^2$. These findings shed
light on the microscopic mechanism underlying photo-induced superconductivity.
They also trace a path towards steady state operation, currently limited by the
availability of a suitable high-repetition rate optical source at these
frequencies. | 2301.08633v2 |
2023-02-13 | Superconductivity with large upper critical field in noncentrosymmetric Cr-bearing high-entropy alloys | A series of new Cr$_{5+x}$Mo$_{35-x}$W$_{12}$Re$_{35}$Ru$_{13}$C$_{20}$
high-entropy alloys (HEAs) have been synthesized and characterized by x-ray
diffraction, scanning electron microscopy, electrical resistivity, magnetic
susceptibility and specific heat measurements. It is found that the HEAs adopt
a noncentrosymmetric cubic $\beta$-Mn type structure and exhibit bulk
superconductivity for 0 $\leq$ $x$ $\leq$ 9. With increasing $x$, the cubic
lattice parameter decreases from 6.7940(3) {\AA} to 6.7516(3) {\AA}. Meanwhile,
the superconducting transition temperature $T_{\rm c}$ is suppressed from 5.49
K to 3.35 K due to the magnetic pair breaking caused by Cr moments. For all
these noncentrosymmetric HEAs, the zero-temperature upper critical field
$B_{\rm c2}$(0) is comparable to Pauli paramagnetic limit $B_{\rm P}$(0) =
1.86$T_{\rm c}$. In particular, the $B_{\rm c2}$(0)/$B_{\rm P}$(0) ratio
reaches a maximum of $\sim$1.03 at $x$ = 6, which is among the highest for
$\beta$-Mn type superconductors. | 2302.06036v1 |
2023-02-23 | Pressure induced electride phase formation in calcium: A key to its strange high-pressure behavior | Elemental calcium (Ca), a simple metal at ambient conditions, has attracted
huge interest because of its unusual high-pressure behavior in structural,
electrical, and melting properties whose origin remain unsolved. Here, using a
theoretical framework appropriate for describing electride phase formation,
i.e., the presence of anionic electrons, we establish electride formation in Ca
at a pressure as low as 8 GPa. Our analysis shows that under pressure the
valence electrons of Ca localize at octahedral holes and exhibit anionic
character which is responsible for its strange pressure behavior. Our
calculated enthalpy and electrical resistance indicate that Ca will directly
transform from an FCC-electride phase to an SC-electride phase near 30 GPa
thereby avoiding the intermediate BCC phase. These findings are not limited to
Ca but might hold a key to the understanding of host-guest type structures
which occur in other elemental solids though at much higher pressures. | 2302.11833v1 |
2023-05-16 | Ambient and high-pressure electrical transport and structural investigations of magnetic Weyl semimetal PrAlGe | We present ambient and high-pressure electrical transport and structural
properties of recently discovered magnetic Weyl semimetal PrAlGe. Electrical
resistivity at ambient pressure shows an anomaly at $T_C$ = 15.1 K related to
the ferromagnetic transition. Anomalous Hall effect (AHE) is observed below
$T_C$. We observe a 1.4 K/GPa increase of $T_C$ with pressure, resulting in
$T_C$ $\approx$ 47 K at 23.0 GPa. Strong competition between Lorentz force and
spin-scattering mechanisms suppressed by magnetic field is deduced from the
magnetoresistance measurements under pressure. As in the ambient pressure case,
the AHE is found to be present below $T_C$ up to the highest applied pressure.
We observe a clear anomaly in the pressure dependence of $T_C$,
magnetoresistance and Hall effect at 12.5 GPa suggesting the occurrence of a
pressure-induced electronic transition at this pressure. X-ray diffraction
(XRD) experiment under pressure revealed the lattice structure to be stable up
to $\sim$19.6 GPa with the absence of any symmetry changing structural phase
transition from the initial $I4_1md$ structure. Careful analysis of the
pressure dependent XRD data reveal an isostructural transition near 11 GPa.
Observed isostructural transition may be related to the pressure-induced
electronic transition deduced from the magnetoresistance and Hall effect data. | 2305.09298v1 |
2023-05-18 | High-quality superconducting α-Ta film sputtered on heated silicon substrate | Intrigued by the discovery of the long lifetime in the
{\alpha}-Ta/Al2O3-based Transmon qubit, researchers recently found {\alpha}-Ta
film is a promising platform for fabricating multi-qubits with long coherence
time. To meet the requirements for integrating superconducting quantum
circuits, the ideal method is to grow {\alpha}-Ta film on a silicon substrate
compatible with industrial manufacturing. Here we report the {\alpha}-Ta film
sputter-grown on Si (100) with a low-loss superconducting TiNx buffer layer.
The {\alpha}-Ta film with a large growth temperature window has a good
crystalline character. The superconducting critical transition temperature (Tc)
and residual resistivity ratio (RRR) in the {\alpha}-Ta film grown at 500
{\deg}C are higher than that in the {\alpha}-Ta film grown at room temperature
(RT). These results provide crucial experimental clues toward understanding the
connection between the superconductivity and the materials' properties in the
{\alpha}-Ta film and open a new route for producing a high-quality {\alpha}-Ta
film on silicon substrate for future industrial superconducting quantum
computers. | 2305.10957v2 |
2023-05-20 | A Computational Approach for Mapping Electrochemical Activity of Multi-Principal Element Alloys | Multi principal element alloys (MPEAs) comprise a unique class of metal
alloys. MPEAs have been demonstrated to possess several exceptional properties,
including, as most relevant to the present study, a high corrosion resistance.
In the context of MPEA design, the vast number of potential alloying elements
and the staggering number of elemental combinations favours a computational
alloy design approach. In order to computationally assess the prospective
corrosion performance of MPEA, an approach was developed in this study. A
density functional theory (DFT) based Monte Carlo method was used for the
development of MPEA structure, with the AlCrTiV alloy used as a model.
High-throughput DFT calculations were performed to create training datasets for
surface activity towards different adsorbate species: O2-, Cl- and H+. Machine
learning (ML) with combined representation was then utilised to predict the
adsorption and vacancy energies as descriptors for surface activity. The
capability of the combined computational methods of MC, DFT and ML, as a
virtual electrochemical performance simulator for MPEAs was established and may
be useful in exploring other MPEAs. | 2305.12059v1 |
2023-06-16 | Epitaxial α-Ta (110) film on a-plane sapphire substrate for superconducting qubits on wafer scale | Realization of practical superconducting quantum computing requires many
qubits of long coherence time. Compared to the commonly used Ta deposited on
c-plane sapphire, which occasionally form {\alpha}-Ta (111) grains and
\b{eta}-tantalum grains, high quality Ta (110) film can grow epitaxial on
a-plane sapphire because of the atomic relationships at the interface.
Well-ordered {\alpha}-Ta (110) film on wafer-scale a-plane sapphire has been
prepared. The film exhibits high residual resistance ratio. Transmon qubits
fabricated using these film shows relaxation times exceeding 150 {\mu}s. The
results suggest Ta film on a-plane sapphire is a promising choice for long
coherence time qubit on wafer scale. | 2306.09568v2 |
2023-08-07 | Modeling of electrochemical oxide film growth -- impact of band-to-band tunneling | The Point Defect Model (PDM) describes the corrosion resistance properties of
oxide films based on interfacial reactions and defect transport, which are
affected by the electric field inside the oxide film. The PDM assumes a
constant electric field strength due to band-to-band tunneling (BTBT) of
electrons and the separation of electrons and holes by high electric fields. In
this manuscript we present a more complex expansion of the common models to
simulate steady state oxide films to test this assumption. The R-PDM was
extended by including the transport of electrons and holes and BTBT. It could
be shown that BTBT only occurs in very rare cases of narrow band gaps and high
electric fields and the impact of electrons and holes does indeed lead to a
buffering effect on the electric field, but does not lead to a constant
electric field strength. Modeling the transport of electrons and holes on the
oxide film allows to specifically estimate their potential impact on the film
growth. Especially during modeling of oxide films with narrow band gap and/or
electrochemical reactions at the film/solution interface the electrons and
holes needs to be included to the model. | 2308.05113v1 |
2023-09-09 | High-throughput screening of coherent topologically close-packed precipitates in hexagonal close-packed metallic systems | The nanoscale, coherent topologically close-packed (TCP) precipitate plates
in magnesium alloys are found beneficial to the strength and creep resistance
of alloys. However, the conventional trial-and-error method is too
time-consuming and costly, which impedes the application of TCP precipitates to
hcp-based metallic alloys. Here, we systematically screen the potential
coherent TCP precipitate plates in the three most common hcp alloys, magnesium
(Mg), titanium (Ti), and zirconium (Zr) alloys, using an efficient
high-throughput screening methodology. Our findings indicate that the
hcp-to-TCP structural transformations readily occur in Mg alloys, leading to
abundant precipitation of TCP plates. However, hcp-Ti and Zr alloys exhibit a
preference for hcp-to-bcc structural transformations, rather than the in situ
precipitation of TCP plates. These screening results are largely consistent
with experimental observations. The insights gained contribute to a deeper
understanding of precipitation behavior in various hcp-based alloys at the
atomic level and provide insightful reference results for designing novel
alloys containing TCP phases. | 2309.04822v2 |
2023-09-18 | Superconductivity in the bcc-type High-entropy Alloy TiHfNbTaMo | X-ray powder diffraction, electrical resistivity, magnetization, and
thermodynamic measurements were conducted to investigate the structure and
superconducting properties of TiHfNbTaMo, a novel high-entropy alloy possessing
a valence electron count (VEC) of 4.8. The TiHfNbTaMo HEA was discovered to
have a body-centered cubic structure and a microscopically homogeneous
distribution of the constituent elements. This material shows type-II
superconductivity with Tc = 3.42 K, lower critical field with 22.8 mT, and
upper critical field with 3.95 T. Low-temperature specific heat measurements
show that the alloy is a conventional s-wave type with a moderately coupled
superconductor. First-principles calculations show that the density of states
(DOS) of the TiHfNbTaMo alloy is dominated by hybrid d orbitals of these five
metal elements. Additionally, the TiHfNbTaMo HEA exhibits three van Hove
singularities. Furthermore, the VEC and the composition of the elements
(especially the Nb elemental content) affect the Tc of the bcc-type HEA. | 2309.09494v1 |
2023-11-26 | On the special oxidation mechanism of a Mg-Y-Al alloy contained LPSO phase at high temperatures | This work investigated the oxidation of Mg-11Y-1Al alloy in Ar-20%O2 at
500{\deg}through multiscale characterization. The results show that the
network-like long-period stacking ordered(LPSO) phase decomposed into a
needle-like LPSO phase and a polygonal Mg24Y5 phase. The needle-like LPSO phase
resulted in the formation of a high-dense of needle-like oxide at the oxidation
front of the area initially occupied by the network-like LPSO phase. The
further inward oxygen would diffuse along the needle-like oxide-matrix
interfaces and react with Y in the surrounding Mg matrix, resulting in the
lateral growth of these needle-like oxides. Finally, the discrete needle-like
oxides were interconnected to form a thicker and continuous oxide scale which
could be more effective in hindering the elemental diffusion. Meanwhile, Al
could partially enter the Y2O3 oxide scale and formed a strengthened (Y,Al)O
oxide scale which could show a greater resistance to cracking and debonding. | 2311.15182v1 |
2024-03-29 | Metamagnetism in the high-pressure tetragonal phase of UTe$_2$ | A structural orthorhombic-to-tetragonal phase transition was recently
discovered in the heavy-fermion compound UTe$_2$ at a pressure
$p^*\simeq3-8$~GPa [Honda \textit{et al.}, J. Phys. Soc. Jpn. \textbf{92},
044702 (2023); Huston \textit{et al.}, Phys. Rev. Mat. \textbf{6}, 114801
(2022)]. In the high-pressure tetragonal phase, a phase transition at
$T_x=235$~K and a superconducting transition at $T_{sc}=2$~K have been
revealed. In this work, we present an electrical-resistivity study of UTe$_2$
in pulsed magnetic fields up to $\mu_0H=58$~T combined with pressures up to $p$
= 6 GPa. The field was applied in a direction tilted by 30~$^\circ$~from
\textbf{b} to \textbf{c} in the orthogonal structure, which is identified as
the direction \textbf{c} of the tetragonal structure. In the tetragonal phase,
the presence of superconductivity is confirmed and signatures of metamagnetic
transitions are observed at the fields $\mu_0H_{x1}=24$~T and
$\mu_0H_{x2}=34$~T and temperatures smaller than $T_x$. We discuss the effects
of uniaxial pressure and we propose that a magnetic ordering drives the
transition at $T_x$. | 2403.20277v1 |
2024-04-17 | Anisotropic Nonsaturating Magnetoresistance Observed in HoMn$_6$Ge$_6$: A Kagome Dirac Semimetal | We report the magnetic and magnetotransport properties and electronic band
structure of the kagome Dirac semimetal HoMn$_6$Ge$_6$. Temperature-dependent
electrical resistivity demonstrates various magnetic-transition-driven
anomalies. Notably, a crossover from negative to positive magnetoresistance
(MR) is observed at around 150 K. While the linear nonsaturating positive MR in
the low-temperature region is mainly driven by the linear Dirac-like band
dispersions as predicted by the first-principles calculations, the negative MR
observed in the high-temperature region is due to the spin-flop type magnetic
transition. Consistent with anisotropic Fermi surface topology, we observe
anisotropic magnetoresistance at low temperatures. A significant anomalous Hall
effect has been noticed at high temperatures in addition to a switching of the
dominant charge carrier from electron to hole at around 215 K. | 2404.11414v2 |
2009-01-15 | Metal-insulator transition and electroresistance in lanthanum/calcium manganites La_<1-x>Ca_<x>MnO_<3> (x = 0-0.5) from voltage-current-temperature surfaces | Of the perovskites, ABX_<3>, a subset of special interest is the family in
which the A site is occupied by a lanthanide ion, the B site by a rare earth
and X is oxygen, as such materials often exhibit a large change in electrical
resistance in a magnetic field, a phenomenon known as "colossal"
magnetoresistance (MR). Two additional phenomena in this family have also drawn
attention: the metal-insulator transition (MIT) and electroresistance (ER). The
MIT is revealed by measuring resistance as a function of temperature, and
observing a change in the sign of the gradient. ER - the dependence of the
resistance on applied current - is revealed by measuring resistance as a
function of applied current. Up until now, the phenomena of MIT and ER have
been treated separately. Here we report simultaneous observation of the MIT and
ER in the lanthanum/calcium manganites. We accomplish this by measuring
voltage-current curves over a wide temperature range (10-300 K) allowing us to
build up an experimental voltage surface over current-temperature axes. These
data directly lead to resistance surfaces. This approach provides additional
insight into the phenomena of electrical transport in the lanthanum/calcium
manganites, in particular the close connection of the maximum ER to the
occurrence of the MIT in those cases of a paramagnetic insulator (PMI) to
ferromagnetic metal (FMM) transition. | 0901.2243v1 |
2009-10-24 | Monte Carlo Study of the Spin Transport in Magnetic Materials | The resistivity in magnetic materials has been theoretically shown to depend
on the spin-spin correlation function which in turn depends on the
magnetic-field, the density of conduction electron, the magnetic ordering
stability, etc. However, these theories involved a lot of approximations, so
their validity remained to be confirmed. The purpose of this work is to show by
extensive Monte Carlo (MC) simulation the resistivity of the spin current from
low-$T$ ordered phase to high-$T$ paramagnetic phase in a ferromagnetic film.
We take into account the interaction between the itinerant spins and the
localized lattice spins as well as the interaction between itinerant spins
themselves. We show that the resistivity undergoes an anomalous behavior at the
magnetic phase transition in agreement with previous theories in spite of their
numerous approximations. The origin of the resistivity peak near the phase
transition in ferromagnets is interpreted here as stemming from the existence
of magnetic domains in the critical region. This interpretation is shown to be
in consistence with previous theoretical pictures. Resistivity in a simple
cubic antiferromagnet is also shown. The absence of a peak in this case is
explained. | 0910.4619v3 |
2021-01-04 | Thermal Resistance at a Twist Boundary and Semicoherent Heterointerface | Traditional models of interfacial phonon scattering, including the acoustic
mismatch model (AMM) and diffuse mismatch model (DMM), take into account the
bulk properties of the material surrounding the interface, but not the atomic
structure and properties of the interface itself. Here, we derive a theoretical
formalism for the phonon scattering at a dislocation grid, or two
interpenetrating orthogonal arrays of dislocations, as this is the most stable
structure of both the symmetric twist boundary and semicoherent
heterointerface. With this approach, we are able to separately examine the
contribution to thermal resistance due to the step function change in acoustic
properties and due to interfacial dislocation strain fields, which induces
diffractive scattering. Both low-angle Si-Si twist boundaries and the Si-Ge
heterointerfaces are considered here and compared to previous experimental and
simulation results. This work indicates that scattering from misfit dislocation
strain fields doubles the thermal boundary resistance of Si-Ge heterointerfaces
compared to scattering due to acoustic mismatch alone. Scattering from grain
boundary dislocation strain fields is predicted to dominate the thermal
boundary resistance of Si-Si twist boundaries. This physical treatment can
guide the thermal design of devices by quantifying the relative importance of
interfacial strain fields, which can be engineered via fabrication and
processing methods, versus acoustic mismatch, which is fixed for a given
interface. Additionally, this approach captures experimental and simulation
trends such as the dependence of thermal boundary resistance on the grain
boundary angle and interfacial strain energy. | 2101.01058v2 |
2015-07-15 | Influence of Periodic Surface Nanopatterning Profiles on Series Resistance in Thin-Film Crystalline Silicon Heterojunction Solar Cells | In the frame of the development of thin crystalline silicon solar cell
technologies, surface nanopatterning of silicon is gaining importance. Its
impact on the material quality is, however, not yet fully controlled.We
investigate here the influence of surface nanotexturing on the series
resistance of a contacting scheme relevant for thin-film crystalline silicon
heterojunction solar cells. Two dimensional periodic nanotextures are
fabricated using a combination of nanoimprint lithography and either dry or wet
etching, while random pyramid texturing is used for benchmarking. We compare
these texturing techniques in terms of their effect on the series resistance of
a solar cell through a study of the sheet resistance (Rsh ) and contact
resistance (Rc) of its front layers, i.e., a sputtered transparent conductive
oxide and evaporated metal contacts. We have found by four-point probe and the
transfer length methods that dry-etched nanopatterns render the highest Rsh and
Rc values. Wet-etched nanopatterns, on the other hand, have less impact on Rc
and render Rsh similar to that obtained from the nontextured case. | 1507.07819v1 |
2023-01-12 | On the switching mechanism and optimisation of ion irradiation enabled 2D $MoS_2$ memristors | Memristors are prominent passive circuit elements with promising futures for
energy-efficient in-memory processing and revolutionary neuromorphic
computation. State-of-the-art memristors based on two-dimensional (2D)
materials exhibit enhanced tunability, scalability and electrical reliability.
However, the fundamental of the switching is yet to be clarified before they
can meet industrial standards in terms of endurance, variability, resistance
ratio, and scalability. This new physical simulator based on the kinetic Monte
Carlo (kMC) algorithm reproduces the defect migration process in 2D materials
and sheds light on the operation of 2D memristors. The present work employs the
simulator to study a two-dimensional $2H-MoS_2$ planar resistive switching (RS)
device with an asymmetric defect concentration introduced by ion irradiation.
The simulations unveil the non-filamentary RS process and propose practical
routes to optimize the device's performance. For instance, the resistance ratio
can be increased by 53% by controlling the concentration and distribution of
defects, while the variability can be reduced by 55% by increasing 5-fold the
device size from 10 to 50 nm. Our simulator also explains the trade-offs
between the resistance ratio and variability, resistance ratio and scalability,
and variability and scalability. Overall, the simulator may enable an
understanding and optimization of devices to expedite cutting-edge
applications. | 2301.05260v2 |
2011-12-13 | Online in-situ X-ray diffraction setup for structural modification studies during swift heavy ion irradiation | The high energy density of electronic excitations due to the impact of swift
heavy ions can induce structural modifications in materials. We present a X-ray
diffractometer called ALIX, which has been set up at the low-energy IRRSUD
beamline of the GANIL facility, to allow the study of structural modification
kinetics as a function of the ion fluence. The X-ray setup has been modified
and optimized to enable irradiation by swift heavy ions simultaneously to X-ray
pattern recording. We present the capability of ALIX to perform simultaneous
irradiation - diffraction by using energy discrimination between X-rays from
diffraction and from ion-target interaction. To illustrate its potential,
results of sequential or simultaneous irradiation - diffraction are presented
in this article to show radiation effects on the structural properties of
ceramics. Phase transition kinetics have been studied during xenon ion
irradiation of polycrystalline MgO and SrTiO3. We have observed that MgO oxide
is radiation-resistant to high electronic excitations, contrary to the high
sensitivity of SrTiO3, which exhibits transition from the crystalline to the
amorphous state during irradiation. By interpreting the amorphization kinetics
of SrTiO3, defect overlapping models are discussed as well as latent track
characteristics. Together with a transmission electron microscopy study, we
conclude that a single impact model describes the phase transition mechanism. | 1112.2832v2 |
2017-10-07 | High pressure x-ray study of spin-Peierls physics in the quantum spin chain material TiOCl | The application of pressure can induce transitions between unconventional
quantum phases in correlated materials. The inorganic compound TiOCl, composed
of chains of S=1/2 Ti ions, is an ideal realization of a spin-Peierls system
with a relatively simple unit cell. At ambient pressure, it is an insulator due
to strong electronic interactions (a Mott insulator). Its resistivity shows a
sudden decrease with increasing pressure, indicating a transition to a more
metallic state which may coincide with the emergence of charge density wave
order. Therefore, high pressure studies of the structure with x-rays are
crucial in determining the ground-state physics in this quantum magnet. In
ambient pressure, TiOCl exhibits a transition to an incommensurate nearly
dimerized state at $T_{c2}=92$ K and to a commensurate dimerized state at
$T_{c1}=66$ K. Here, we discover a rich phase diagram as a function of
temperature and pressure using x-ray diffraction on a single crystal in a
diamond anvil cell down to $T=4$ K and pressures up to 14.5 GPa. Remarkably,
the magnetic interaction scale increases dramatically with increasing pressure,
as indicated by the high onset temperature of the spin-Peierls phase. At
$\sim$7 GPa, the extrapolated onset of the spin-Peierls phase occurs above
$T=300$ K, indicating a quantum singlet state exists at room temperature.
Further comparisons are made with the phase diagrams of related spin-Peierls
systems that display metallicity and superconductivity under pressure. | 1710.02632v1 |
2019-02-28 | Quenched nematic criticality separating two superconducting domes in an iron-based superconductor under pressure | The nematic electronic state and its associated nematic critical fluctuations
have emerged as potential candidates for superconducting pairing in various
unconventional superconductors. However, in most materials their coexistence
with other magnetically-ordered phases poses significant challenges in
establishing their importance. Here, by combining chemical and hydrostatic
physical pressure in FeSe$_{0.89}$S$_{0.11}$, we provide a unique access to a
clean nematic quantum phase transition in the absence of a long-range magnetic
order. We find that in the proximity of the nematic phase transition, there is
an unusual non-Fermi liquid behavior in resistivity at high temperatures that
evolves into a Fermi liquid behaviour at the lowest temperatures. From quantum
oscillations in high magnetic fields, we trace the evolution of the Fermi
surface and electronic correlations as a function of applied pressure. We
detect experimentally a Lifshitz transition that separates two distinct
superconducting regions: one emerging from the nematic electronic phase with a
small Fermi surface and strong electronic correlations and the other one with a
large Fermi surface and weak correlations that promotes nesting and
stabilization of a magnetically-ordered phase at high pressures. The lack of
mass divergence suggests that the nematic critical fluctuations are quenched by
the strong coupling to the lattice. This establishes that superconductivity is
not enhanced at the nematic quantum phase transition in the absence of magnetic
order. | 1902.11276v1 |
2020-09-03 | Topological Nature of High Temperature Superconductivity | The key to unraveling the nature of high-temperature superconductivity (HTS)
lies in resolving the enigma of the pseudogap state. The pseudogap state in the
underdoped region is a distinct thermodynamic phase characterized by
nematicity, temperature-quadratic resistive behavior, and magnetoelectric
effects. Till present, a general description of the observed universal features
of the pseudogap phase and their connection with HTS was lacking. The proposed
work constructs a unifying effective field theory capturing all universal
characteristics of HTS materials and explaining the observed phase diagram. The
pseudogap state is established to be a phase where a charged magnetic monopole
condensate confines Cooper pairs to form an oblique version of a
superinsulator. The HTS phase diagram is dominated by a tricritical point (TCP)
at which the first order transition between a fundamental Cooper pair
condensate and a charged magnetic monopole condensate merges with the
continuous superconductor-normal metal and superconductor-pseudogap state phase
transitions. The universality of the HTS phase diagram reflects a unique
topological mechanism of competition between the magnetic monopole condensate,
inherent to antiferromagnetic-order-induced Mott insulators and the Cooper pair
condensate. The obtained results establish the topological nature of the HTS
and provide a platform for devising materials with the enhanced superconducting
transition temperature. | 2009.01763v2 |
2020-09-16 | Tailoring c-axis orientation in epitaxial Ruddlesden-Popper Pr$_{0.5}$Ca$_{1.5}$MnO$_{4}$ films | Interest for layered Ruddlesden-Popper strongly correlated manganites of
Pr$_{0.5}$Ca$_{1.5}$MnO$_4$ as well as to their thin film polymorphs is
motivated by the high temperature of charge orbital ordering above room
temperature. We report on the tailoring of the c-axis orientation in epitaxial
RP-PCMO films grown on SrTiO$_3$ (STO) substrates with different orientations
as well as the use of CaMnO$_3$ (CMO) buffer layers. Films on STO(110) reveal
in-plane alignment of the c-axis lying along to the [100] direction. On
STO(100), two possible directions of the in-plane c-axis lead to a mosaic like,
quasi two-dimensional nanostructure, consisting of RP, rock-salt and perovskite
building blocks. With the use of a CMO buffer layer, RP-PCMO epitaxial films
with c-axis out-of-plane were realized. Different physical vapor deposition
techniques, i.e. ion beam sputtering (IBS), pulsed laser deposition (PLD) as
well as metalorganic aerosol deposition (MAD) are applied in order to
distinguish between the effect of growth conditions and intrinsic epitaxial
properties. For all deposition techniques, despite their very different growth
conditions, the surface morphology, crystal structure and orientation of the
thin films reveal a high level of similarity as verified by X-ray diffraction,
scanning and high resolution transmission electron microscopy. We found that
for different epitaxial relations the stress in the films can be relaxed by
means of a modified interface chemistry. The charge ordering in the films
estimated by resistivity measurements occurs at a temperature close to that
expected in bulk material. | 2009.07523v1 |
2020-09-28 | Pressure-induced reconstructive phase transition in Cd$_3$As$_2$ | Cadmium arsenide Cd$_3$As$_2$ hosts massless Dirac electrons in its
ambient-conditions tetragonal phase. We report X-ray diffraction and electrical
resistivity measurements of Cd$_3$As$_2$ upon cycling pressure beyond the
critical pressure of the tetragonal phase and back to ambient conditions. We
find that at room temperature the transition between the low- and high-pressure
phases results in large microstrain and reduced crystallite size both on rising
and falling pressure. This leads to non-reversible electronic properties
including self-doping associated with defects and a reduction of the electron
mobility by an order of magnitude due to increased scattering. Our study
indicates that the structural transformation is sluggish and shows a sizable
hysteresis of over 1~GPa. Therefore, we conclude that the transition is
first-order reconstructive, with chemical bonds being broken and rearranged in
the high-pressure phase. Using the diffraction measurements we demonstrate that
annealing at ~200$^\circ$C greatly improves the crystallinity of the
high-pressure phase. We show that its Bragg peaks can be indexed as a primitive
orthorhombic lattice with a_HP~8.68 A b_HP~17.15 A and c_HP~18.58 A. The
diffraction study indicates that during the structural transformation a new
phase with another primitive orthorhombic structure may be also stabilized by
deviatoric stress, providing an additional venue for tuning the unconventional
electronic states in Cd3As2. | 2009.13228v2 |
2016-03-01 | Superconductivity in HfTe5 Induced via Pressures | Recently, ZrTe5 and HfTe5 are theoretically studied to be the most promising
layered topological insulators since they are both interlayer weakly bonded
materials and also with a large bulk gap in the single layer. It paves a new
way for the study of novel topological quantum phenomenon tuned via external
parameters. Here, we report the discovery of superconductivity and properties
evolution in HfTe5 single crystal induced via pressures. Our experiments
indicated that anomaly resistance peak moves to low temperature first before
reverses to high temperature followed by disappearance which is opposite to the
low pressure effect on ZrTe5. HfTe5 became superconductive above ~5.5 GPa up to
at least 35 GPa in the measured range. The highest superconducting transition
temperature (Tc) around 5 K was achieved at 20 GPa. High pressure Raman
revealed that new modes appeared around pressure where superconductivity
occurs. Crystal structure studies shown that the superconductivity is related
to the phase transition from Cmcm structure to monoclinic C2/m structure. The
second phase transition from C2/m to P-1 structure occurs at 12 GPa. The
combination of transport, structure measurement and theoretical calculations
enable a completely phase diagram of HfTe5 at high pressures. | 1603.00514v1 |
2021-01-29 | Tunable Doping of Rhenium and Vanadium into Transition Metal Dichalcogenides for Two-Dimensional Electronics | Two-dimensional (2D) transition metal dichalcogenides (TMDCs) with unique
electrical properties are fascinating materials used for future electronics.
However, the strong Fermi level pinning effect at the interface of TMDCs and
metal electrodes always leads to high contact resistance, which seriously
hinders their application in 2D electronics. One effective way to overcome this
is to use metallic TMDCs or transferred metal electrodes as van der Waals (vdW)
contacts. Alternatively, using highly conductive doped TMDCs will have a
profound impact on the contact engineering of 2D electronics. Here, a novel
chemical vapor deposition using mixed molten salts is established for
vapor-liquid-solid growth of high-quality rhenium (Re) and vanadium (V)-doped
TMDC monolayers with high controllability and reproducibility. A tunable
semiconductor to metal transition is observed in the Re and V-doped TMDCs.
Electrical conductivity increases up to a factor of 108 in the degenerate
V-doped WS2 and WSe2. Using V-doped WSe2 as vdW contact, the on-state current
and on/off ratio of WSe2-based field-effect transistors have been substantially
improved (from ~10-8 to 10-5 A; ~104 to 108), compared to metal contacts.
Future studies on lateral contacts and interconnects using doped TMDCs will
pave the way for 2D integrated circuits and flexible electronics. | 2101.12423v1 |
2020-11-05 | Temperature-dependent elastic properties of binary and multicomponent high-entropy refractory carbides | Available information concerning the elastic moduli of refractory carbides at
temperatures (T) of relevance for practical applications is sparse and/or
inconsistent. We carry out ab initio molecular dynamics (AIMD) simulations at T
= 300, 600, 900, and 1200 K to determine the temperature-dependences of the
elastic constants of rocksalt-structure (B1) TiC, ZrC, HfC, VC, and TaC
compounds as well as multicomponent high-entropy carbides (Ti,Zr,Hf,Ta,W)C and
(V,Nb,Ta,Mo,W)C. The second order elastic constants are calculated by
least-square fitting of the analytical expressions of stress vs. strain
relationships to simulation results obtained from three tensile and three shear
deformation modes. Moreover, we employ sound velocity measurements to evaluate
the bulk, shear, elastic moduli and Poisson's ratios of single-phase B1
(Ti,Zr,Hf,Ta,W)C and (V,Nb,Ta,Mo,W)C at ambient conditions. Our experimental
results are in excellent agreement with the values obtained by AIMD
simulations. In comparison with the predictions of previous ab initio
calculations - where the extrapolation of finite-temperature elastic properties
accounted for thermal expansion while neglecting intrinsic vibrational effects
- AIMD simulations produce a softening of elastic moduli with T in closer
agreement with experiments. Results of our simulations show that TaC is the
system which exhibits the highest elastic resistances to both tensile and shear
deformation up to 1200 K, and identify the high-entropy (V,Nb,Ta,Mo,W)C system
as candidate for applications that require good ductility and toughness at room
as well as elevated temperatures. | 2011.02742v1 |
2021-03-09 | Crack-free caustic magnesia-bonded refractory castables | A growing interest in designing high-alumina MgO-bonded refractory castables
has been identified in recent years due to the magnesia ability to react: (i)
with water at the initial processing stages of these materials (inducing the
precipitation of brucite phase) or (ii) with alumina, giving rise to in situ
MgAl2O4 generation at high temperatures. Nevertheless, despite the great
potential of caustic magnesia to be used as a binder in such systems due to its
high reactivity, it is still a challenge to control the hydration reaction rate
of this oxide and the negative effects derived from the expansive feature of
Mg(OH)2 formation. Thus, this work evaluated the incorporation of different
contents of aluminum hydroxyl lactate (AHL) into caustic magnesia-bonded
castables, aiming to control the brucite precipitation during the curing and
drying steps of the prepared samples, resulting in crack-free refractories. The
designed compositions were characterized via flowability, setting behavior,
X-ray diffraction, cold flexural strength, porosity, permeability and
thermogravimetric measurements. According to the results, instead of Mg(OH)2,
hydrotalcite-like phases [Mg6Al2(OH)16(OH)2.4.5H2O and Mg6Al2(OH)16(CO3).4H2O]
were the main hydrated phases identified in the AHL-containing compositions.
The addition of 1.0 wt.% of aluminum hydroxyl lactate to the designed castable
proved to be, so far, the best option for this magnesia source, resulting in
the development of a crack-free refractory with enhanced properties and greater
spalling resistance under heating. | 2103.05361v1 |
2021-03-20 | Towards Superior High Temperature Properties in Low Density AlCrFeNiTi Compositionally Complex Alloys | Three novel precipitation strengthened bcc alloys which exhibit a smooth
microstructural gradient with composition have been fabricated in bulk form by
induction casting. All three alloys are comprised of a mixture of disordered
A2-(Fe, Cr) and L2$_1$-ordered (Ni, Fe)$_{2}$AlTi type phases both as-cast and
after long-term annealing at 900 $^{\circ}$C. The ratio of disordered to
ordered phase, primary dendrite fraction, and overall microstructural
coarseness all decrease as Cr is replaced by Al and Ti. Differences in phase
composition are quantified through domain averaged principal component analysis
of energy dispersive spectroscopy data obtained during scanning transmission
electron microscopy. Bulk tensile testing reveals retained strengths of nearly
250 MPa up to 900 $^{\circ}$C for the alloys which contain a nanoscale
maze-like arrangement of ordered and disordered phases. One alloy, containing a
duplex microstructure with ductile dendritic regions and highly creep resistant
interdendritic regions, shows a promising balance between high temperature
ductility and strength. For this alloy, tension creep testing was carried out
at 700, 750, and 800 $^{\circ}$C for a broad range of loading conditions and
revealed upper bound creep rates which surpass similar ferritic superalloys and
rival those of several conventionally employed high temperature structural
alloys, including Inconel 617 and 718, at much lower density and raw material
cost. | 2103.11173v1 |
2021-06-02 | Dopant redistribution and activation in Ga ion-implanted high Ge content SiGe by explosive crystallization during UV nanosecond pulsed laser annealing | Explosive crystallization (EC) is often observed when using nanosecond-pulsed
melt laser annealing (MLA) in amorphous silicon (Si) and germanium (Ge). The
solidification velocity in EC is so fast that a diffusion-less crystallization
can be expected. In the contacts of advanced transistors, the active level at
the metal/semiconductor Schottky interface must be very high to achieve a
sub-10^{-9} ohm.cm2 contact resistivity, which has been already demonstrated by
using the dopant surface segregation induced by MLA. However, the beneficial
layer of a few nanometers at the surface may be easily consumed during
subsequent contact cleaning and metallization. EC helps to address such kind of
process integration issues, enabling the optimal positioning of the peak of the
dopant chemical profile. However, there is a lack of experimental studies of EC
in heavily-doped semiconductor materials. Furthermore, to the best of our
knowledge, dopant activation by EC has never been experimentally reported. In
this paper, we present dopant redistribution and activation by an EC process
induced by UV nanosecond-pulsed MLA in heavily gallium (Ga) ion-implanted high
Ge content SiGe. Based on the obtained results, we also highlight potential
issues of integrating EC into real device fabrication processes and discuss how
to manage them. | 2106.00946v1 |
2022-06-29 | Designing wake-up free ferroelectric capacitors based on the $\mathrm{HfO_2/ZrO_2}$ superlattice structure | The wake-up phenomenon widely exists in hafnia-based ferroelectric
capacitors, which causes device parameter variation over time. Crystallization
at higher temperatures have been reported to be effective in eliminating
wake-up, but high temperature may yield the monoclinic phase or generate high
concentration oxygen vacancies. In this work, a unidirectional annealing method
is proposed for the crystallization of $\mathrm{Hf_{0.5}Zr_{0.5}O_2}$ (HZO)
superlattice ferroelectrics, which involves heating from the
$\mathrm{Pt/ZrO_2}$ interface side. Nanoscale $\mathrm{ZrO_2}$ is selected to
resist the formation of monoclinic phase, and the chemically inert Pt electrode
can avoid the continuous generation of oxygen vacancies during annealing. It is
demonstrated that $\mathrm{600^oC}$ annealing only leads to a moderate content
of monoclinic phase in HZO, and the TiN/HZO/Pt capacitor exhibits wake-up free
nature and a $2P_\mathrm{r}$ value of 27.4 $\mu\mathrm{C/cm^2}$. On the other
hand, heating from the $\mathrm{TiN/HfO_2}$ side, or using $\mathrm{500^oC}$
annealing temperature, both yield ferroelectric devices that require a wake-up
process. The special configuration of $\mathrm{Pt/ZrO_2}$ is verified by
comparative studies with several other superlattice structures and HZO
solid-state solutions. It is discovered that heating from the
$\mathrm{Pt/HfO_2}$ side at $\mathrm{600^oC}$ leads to high leakage current and
a memristor behavior. The mechanisms of ferroelectric phase stabilization and
memristor formation have been discussed. The unidirectional heating method can
also be useful for other hafnia-based ferroelectric devices. | 2206.14393v1 |
2022-09-06 | Silicide-based Josephson field effect transistors for superconducting qubits | Scalability in the fabrication and operation of quantum computers is key to
move beyond the NISQ era. So far, superconducting transmon qubits based on
aluminum Josephson tunnel junctions have demonstrated the most advanced
results, though this technology is difficult to implement with large-scale
facilities. An alternative "gatemon" qubit has recently appeared, which uses
hybrid superconducting/semiconducting (S/Sm) devices as gate-tuned Josephson
junctions. Current implementations of these use nanowires however, of which the
large-scale fabrication has not yet matured either. A scalable gatemon design
could be made with CMOS Josephson Field-Effect Transistors as tunable weak
link, where an ideal device has leads with a large superconducting gap that
contact a short channel through high-transparency interfaces. High
transparency, or low contact resistance, is achieved in the microelectronics
industry with silicides, of which some turn out to be superconducting. The
first part of the experimental work in this thesis covers material studies on
two such materials: $\text{V}_3\text{Si}$ and PtSi, which are interesting for
their high $T_\text{c}$, and mature integration, respectively. The second part
covers experimental results on 50 nm gate length PtSi transistors, where the
transparency of the S/Sm interfaces is modulated by the gate voltage. At low
voltages, the transport shows no conductance at low energy, and well-defined
features at the superconducting gap. The barrier height at the S/Sm interface
is reduced by increasing the gate voltage, until a zero-bias peak appears
around zero drain voltage, which reveals the appearance of an Andreev current.
The successful gate modulation of Andreev current in a silicon-based transistor
represents a step towards fully CMOS-integrated superconducting quantum
computers. | 2209.02721v1 |
2023-03-21 | Thermal decoupling in high-$T_c$ cuprate superconductors | Although many years have passed since the discovery of
high-critical-temperature (high-$T_c$) superconducting materials, the
underlying mechanism is still unknown. The B1g phonon anomaly in high-Tc
cuprate superconductors has long been studied; however, the correlation between
the B1g phonon anomaly and superconductivity has yet to be clarified. In the
present study, we successfully reproduced the B1g phonon anomaly in
YBa$_2$Cu$_3$O$_7$ (YBCO) using an ab initio molecular dynamics (AIMD)
simulation and temperature-dependent effective potential (TDEP) method. The Ag
phonon by Ba atoms shows a more severe anomaly than the B1g phonon at low
temperatures. Our analysis of the phonon anomaly and the temperature-dependent
phonon dispersion indicated that decoupling between thermal phenomena and
electron transport at low temperatures leads to layer-by-layer thermal
decoupling in YBCO. Electronically and thermally isolated Ba atoms in YBCO are
responsible for the thermal decoupling. The analytic study of the thermal
dcoupling revealed that Planckian dissipation expressing linear-T resistivity
is another expression of the Fermi liquid of the CuO$_2$ plane. The Uemura plot
of the relationship between Tc and the Fermi temperature, as well as the
superconducting dome in YBCO, is explained rigorously and quantitatively. Our
findings not only present a new paradigm for understanding high-Tc
superconductivity but also imply that the spontaneous formation of
low-temperature layers in materials can lead to revolutionary changes in the
thermal issues of industrial fields. | 2303.11600v1 |
2023-03-24 | A review on the advancements in the characterization of the high-pressure properties of iodates | The goal of this work is to report a systematic and balanced review of the
progress made in recent years on the high-pressure behavior of iodates, a group
of materials with multiple technological applications and peculiar behaviors
under external compression. This review article presents results obtained from
multiple characterization techniques which include: X-ray diffraction, Raman
and infrared spectroscopy, optical-absorption, resistivity, and second-harmonic
generation measurements. The discussion of the results from experiments will be
combined with density-functional theory calculations which have been shown to
be a very useful tool for the interpretation of experimental data. Throughout
the manuscript many of the phenomena observed will be connected to the presence
of a lone electron pairs of the iodine atoms in the studied iodates. The
presence of the lone electron pairs plays a crucial role in the high-pressure
behavior of iodates and it is associated with many of the phenomena discussed
here, in particular with the pressure-induced changes in the character of
iodine-oxygen bonds, which causes many physical properties to behave
nonlinearly. Towards the end of this review, a discussion of current problems
that remain unsolved is presented as well as proposals for possible avenues for
future studies. | 2303.14215v1 |
2023-11-22 | Durable, ultrathin, and antifouling polymer brush coating for efficient condensation heat transfer | Heat exchangers are made of metals because of their high heat conductivity
and mechanical stability. Metal surfaces are inherently hydrophilic, leading to
inefficient filmwise condensation. It is still a challenge to coat these metal
surfaces with a durable, robust and thin hydrophobic layer, which is required
for efficient dropwise condensation. Here, we report the non-structured and
ultrathin (~6 nm) polydimethylsiloxane (PDMS) brushes on copper that sustain
high-performing dropwise condensation in high supersaturation. Due to the
flexible hydrophobic siloxane polymer chains, the coating has low resistance to
drop sliding and excellent chemical stability. The PDMS brushes can sustain
dropwise condensation for up to ~8 h during exposure to 111 {\deg}C saturated
steam flowing at 3 m/s, with a 5-7 times higher heat transfer coefficient
compared to filmwise condensation. The surface is self-cleaning and can reduce
bacterial attachment by 99%. This low-cost, facile, fluorine-free, and scalable
method is suitable for a great variety of condensation heat transfer
applications. | 2311.13353v1 |
2023-12-01 | Insulator to Metal Transition, Spin-Phonon Coupling, and Potential Magnetic Transition Observed in Quantum Spin Liquid Candidate LiYbSe$_2$ under High Pressure | Metallization of quantum spin liquid (QSL) materials has long been considered
as a potential route to achieve unconventional superconductivity. Here we
report our endeavor in this direction by pressurizing a three-dimensional QSL
candidate, LiYbSe$_2$, with a previously unreported pyrochlore structure.
High-pressure X-ray diffraction and Raman studies up to 50 GPa reveal no
appreciable changes of structural symmetry or distortion in this pressure
range. This compound is so insulating that its resistance decreases below
10$^5$ ${\Omega}$ only at pressures above 25 GPa in the corresponding
temperature range accompanying the gradual reduction of band gap upon
compression. Interestingly, an insulator-to-metal transition takes place in
LiYbSe$_2$ at about 68 GPa and the metallic behavior remains up to 123.5 GPa,
the highest pressure reached in the present study. A possible sign of magnetic
or other phase transition was observed in LiYbSe$_2$. The insulator-to-metal
transition in LiYbSe$_2$ under high pressure makes it an ideal system to study
the pressure effects on QSL candidates of spin-1/2 Yb$^{3+}$ system in
different lattice patterns. | 2312.00270v2 |
2024-01-06 | Endless Dirac nodal lines and high mobility in kagome semimetal Ni3In2Se2 single crystal | Kagome-lattice crystal is crucial in quantum materials research, exhibiting
unique transport properties due to its rich band structure and the presence of
nodal lines and rings. Here, we investigate the electronic transport properties
and perform first-principles calculations for Ni$_{3}$In$_{2}$Se$_{2}$ kagome
topological semimetal. First-principle calculations indicate six endless Dirac
nodal lines and two nodal rings with a $\pi$-Berry phase in the
Ni$_{3}$In$_{2}$Se$_{2}$ compound. The temperature-dependent resistivity is
dominated by two scattering mechanisms: $s$-$d$ interband scattering occurs
below 50 K, while electron-phonon ($e$-$p$) scattering is observed above 50 K.
The magnetoresistance (MR) curve aligns with the theory of extended Kohler's
rule, suggesting multiple scattering origins and temperature-dependent carrier
densities. A maximum MR of 120\% at 2 K and 9 T, with a maximum estimated
mobility of approximately 3000 cm$^{2}$V$^{-1}$s$^{-1}$ are observed. The Ni
atom's hole-like d$_{x^{2}-y^{2} }$ and electron-like d$_{z^{2}}$ orbitals
exhibit peaks and valleys, forming a local indirect-type band gap near the
Fermi level (E$_{F}$). This configuration enhances the motion of electrons and
holes, resulting in high mobility and relatively high magnetoresistance. | 2401.03130v1 |
2024-04-18 | Omnidirectional 3D printing of PEDOT:PSS aerogels with tunable electromechanical performance for unconventional stretchable interconnects and thermoelectrics | The next generation of soft electronics will expand to the third dimension.
This will require the integration of mechanically-compliant three-dimensional
functional structures with stretchable materials. This study demonstrates
omnidirectional direct ink writing (DIW) of Poly(3,4-ethylenedioxythiophene)
polystyrene sulfonate (PEDOT:PSS) aerogels with tunable electrical and
mechanical performance, which can be integrated with soft substrates. Several
PEDOT:PSS hydrogels were formulated for DIW and freeze-dried directly on
stretchable substrates to form integrated aerogels displaying high shape
fidelity and minimal shrinkage. The effect of additives and processing in the
PEDOT:PSS hydro and aerogels morphology, and the link with their
electromechanical properties was elucidated. This technology demonstrated
3D-structured stretchable interconnects and planar thermoelectric generators
(TEGs) for skin electronics, as well as vertically-printed high aspect ratio
thermoelectric pillars with a high ZT value of 3.2 10^-3 and ultra-low thermal
conductivity of 0.065 W/(m K). Despite their comparatively low ZT, the aerogel
pillars outpowered their dense counterparts in realistic energy harvesting
scenarios where contact resistances cannot be ignored, and produced up to 26
nW/cm2 (corresponding to a gravimetric power density of 0.76 mW/kg) for a
difference of temperature of 15 K. This work suggests promising advancements in
soft and energy-efficiency electronic systems relevant to soft robotics and
wearable. | 2404.12254v1 |
2024-05-21 | Pick-and-place transfer of arbitrary-metal electrodes for van der Waals device fabrication | Van der Waals electrode integration is a promising strategy to create
near-perfect interfaces between metals and two-dimensional materials, with
advantages such as eliminating Fermi-level pinning and reducing contact
resistance. However, the lack of a simple, generalizable pick-and-place
transfer technology has greatly hampered the wide use of this technique. We
demonstrate the pick-and-place transfer of pre-fabricated electrodes from
reusable polished hydrogenated diamond substrates without the use of any
surface treatments or sacrificial layers. The technique enables transfer of
large-scale arbitrary metal electrodes, as demonstrated by successful transfer
of eight different elemental metals with work functions ranging from 4.22 to
5.65 eV. The mechanical transfer of metal electrodes from diamond onto van der
Waals materials creates atomically smooth interfaces with no interstitial
impurities or disorder, as observed with cross-sectional high-resolution
transmission electron microscopy and energy-dispersive X-ray spectroscopy. As a
demonstration of its device application, we use the diamond-transfer technique
to create metal contacts to monolayer transition metal dichalcogenide
semiconductors with high-work-function Pd, low-work-function Ti, and semi metal
Bi to create n- and p-type field-effect transistors with low Schottky barrier
heights. We also extend this technology to other applications such as ambipolar
transistor and optoelectronics, paving the way for new device architectures and
high-performance devices. | 2405.12830v1 |
2013-08-15 | Spin heat accumulation induced by tunneling from a ferromagnet | An electric current from a ferromagnet into a non-magnetic material can
induce a spin-dependent electron temperature. Here it is shown that this spin
heat accumulation, when created by tunneling from a ferromagnet, produces a
non-negligible voltage signal that is comparable to that due to the coexisting
electrical spin accumulation and can give a different Hanle spin precession
signature. The effect is governed by the spin polarization of the Peltier
coefficient of the tunnel contact, its Seebeck coefficient, and the spin heat
resistance of the non-magnetic material, which is related to the electrical
spin resistance by a spin-Wiedemann-Franz law. Moreover, spin heat injection is
subject to a heat conductivity mismatch that is overcome if the tunnel
interface has a sufficiently large resistance. | 1308.3365v2 |
2015-08-21 | In-Plane fracture of laminated fiber reinforced composites with varying fracture resistance: experimental observations and numerical crack propagation simulations | A series of experimental results on the in-plane fracture of a fiber
reinforced laminated composite panel is analyzed using the variational
multi-scale cohesive method (VMCM). The VMCM results demonstrate the influence
of specimen geometry and load distribution on the propagation of large scale
bridging cracks in the fiber reinforced panel. Experimentally observed
variation in fracture resistance is substantiated numerically by comparing the
experimental and VMCM load-displacement responses of geometrically scaled
single edge-notch three point bend (SETB) specimens. The results elucidate the
size dependence of the traction-separation relationship for this class of
materials even in moderately large specimens, contrary to the conventional
understanding of it being a material property. The existence of a "free
bridging zone" (different from the conventional "full bridging zone") is
recognized, and its influence on the evolving fracture resistance is discussed.
The numerical simulations and ensuing bridging zone evolution analysis
demonstrates the versatility of VMCM in objectively simulating progressive
crack propagation, compared against conventional numerical schemes like
traditional cohesive zone modeling, which require a priori knowledge of the
crack path. | 1508.06220v1 |
2016-06-17 | Atomically-thin Ohmic Edge Contacts Between Two-dimensional Materials | With the decrease of the dimensions of electronic devices, the role played by
electrical contacts is ever increasing, eventually coming to dominate the
overall device volume and total resistance. This is especially problematic for
monolayers of semiconducting transition metal dichalcogenides (TMDs), which are
promising candidates for atomically thin electronics. Ideal electrical contacts
to them would require the use of similarly thin electrode materials while
maintaining low contact resistances. Here we report a scalable method to
fabricate ohmic graphene edge contacts to two representative monolayer TMDs -
MoS2 and WS2. The graphene and TMD layer are laterally connected with
wafer-scale homogeneity, no observable overlap or gap, and a low average
contact resistance of 30 k$\Omega$ $\mu$m. The resulting graphene edge contacts
show linear current-voltage (IV) characteristics at room temperature, with
ohmic behavior maintained down to liquid helium temperatures. | 1606.05393v1 |
2017-10-04 | A phononic switch based on ferroelectric domain walls | The ease with which domain walls (DWs) in ferroelectric materials can be
written and erased provides a versatile way to dynamically modulate heat
fluxes. In this work we evaluate the thermal boundary resistance (TBR) of
180$^{\circ}$ DWs in prototype ferroelectric perovskite PbTiO$_3$ within the
numerical formalisms of nonequilibrium molecular dynamics and nonequilibrium
Green's functions. An excellent agreement is obtained for the TBR of an
isolated DW derived from both approaches, which reveals the harmonic character
of the phonon-DW scattering mechanism. The thermal resistance of the
ferroelectric material is shown to increase up to around 20%, in the system
sizes here considered, due to the presence of a single DW, and larger
resistances can be attained by incorporation of more DWs along the path of
thermal flux. These results, obtained at device operation temperatures, prove
the viability of an electrically actuated phononic switch based on
ferroelectric DWs. | 1710.01574v1 |
2019-09-13 | Theory of anisotropic elastoresistivity of two-dimensional extremely strongly correlated metals | There is considerable recent interest in the phenomenon of anisotropic
electroresistivity of correlated metals. While some interesting work has been
done on the iron-based superconducting systems, not much is known for the
cuprate materials. Here we study the anisotropy of elastoresistivity for
cuprates in the normal state. We present theoretical results for the effect of
strain on resistivity, and additionally on the optical weight and local density
of states. We use the recently developed extremely strongly correlated Fermi
liquid theory in two dimensions, which accounts quantitatively for the
unstrained resistivities for three families of single-layer cuprates. The
strained hoppings of a tight-binding model are roughly modeled analogously to
strained transition metals. The strained resistivity for a two-dimensional
$t$-$t'$-$J$ model are then obtained, using the equations developed in recent
work. Our quantitative predictions for these quantities have the prospect of
experimental tests in the near future, for strongly correlated materials such
as the hole-doped and electron-doped high-$T_c$ materials. | 1909.06471v4 |
2020-09-04 | Relation between resistance drift and optical gap in phase change materials | The optical contrast in a phase change material is concomitant with its
structural transition. We connect these two by first recognizing that Friedel
oscillations couple electrons propagating in opposite directions and supply an
additional Coulomb energy. As the crystal switches phase, this energy acquires
time dependence and the Landau-Zener mechanism operates, steering population
transfer from the valence to the conduction band and vice versa. Spectroscopy
suggests that the oscillator energy dominates the optical properties and a
calculation involving the crystalline field and spin-orbit interaction yields
good estimates for of both structural phases. Further analysis relates the
optical gap with the crystalline-field energy as well as activation energy for
electrical conduction. This last property characterizes the amorphous phase,
thereby furnishing a link between the crystalline field and the activation
energy and ultimately with the resistance drift exponent. Providing optical
means to quantify resistance drift in PCMs could circumvent the need for
fabricating expensive devices and performing time consuming measurements. | 2009.02048v1 |
2017-05-23 | Reducing Graphene Device Variability with Yttrium Sacrificial Layers | Graphene technology has made great strides since the material was isolated
more than a decade ago. However, despite improvements in growth quality and
numerous 'hero' devices, challenges of uniformity remain, restricting
large-scale development of graphene-based technologies. Here we investigate and
reduce the variability of graphene transistors by studying the effects of
contact metals (with and without Ti layer), resist, and yttrium (Y) sacrificial
layers during the fabrication of hundreds of devices. We find that with optical
photolithography, residual resist and process contamination is unavoidable,
ultimately limiting device performance and yield. However, using Y sacrificial
layers to isolate the graphene from processing conditions improves the yield
(from 73% to 97%), average device performance (three-fold increase of mobility,
58% lower contact resistance), and the device-to-device variability (standard
deviation of Dirac voltage reduced by 20%). In contrast to other sacrificial
layer techniques, removal of the Y sacrificial layer with HCl does not harm
surrounding materials, simplifying large-scale graphene fabrication. | 1705.09388v1 |
2019-10-24 | Magneto-memristive switching in a two-dimensional layer antiferromagnet | Memristive devices whose resistance can be hysteretically switched by
electric field or current are intensely pursued both for fundamental interest
as well as potential applications in neuromorphic computing and phase-change
memory. When the underlying material exhibits additional charge or spin order,
the resistive states can be directly coupled, further allowing for electrical
control of the collective phases. Here, we report the observation of abrupt,
memristive switching of tunneling current in nanoscale junctions of ultrathin
CrI$_3$, a natural layer antiferromagnet. The coupling to spin order enables
both tuning of the resistance hysteresis by magnetic field, and electric-field
switching of magnetization even in multilayer samples. | 1910.11383v1 |
2019-11-14 | Nonvolatile Resistive Switching in Nanocrystalline Molybdenum Disulfide with Ion-Based Plasticity | Non-volatile resistive switching is demonstrated in memristors with
nanocrystalline molybdenum disulfide (MoS$_2$) as the active material. The
vertical heterostructures consist of silicon, vertically aligned MoS$_2$ and
chrome / gold metal electrodes. Electrical characterizations reveal a bipolar
and forming free switching process with stable retention for at least 2500
seconds. Controlled experiments carried out in ambient and vacuum conditions
suggest that the observed resistive switching is based on hydroxyl ions
(OH$^-$). These originate from catalytic splitting of adsorbed water molecules
by MoS$_2$. Experimental results in combination with analytical simulations
further suggest that electric field driven movement of the mobile OH$^-$ ions
along the vertical MoS$_2$ layers influences the energy barrier at the
Si/MoS$_2$ interface. The scalable and semiconductor production compatible
device fabrication process used in this work offers the opportunity to
integrate such memristors into existing silicon technology for future
neuromorphic applications. The observed ion-based plasticity may be exploited
in ionicelectronic devices based on TMDs and other 2D materials for memristive
applications. | 1911.06032v1 |
2023-02-20 | Extraordinary Bulk Insulating Behavior in the Strongly Correlated Materials FeSi and FeSb$_2$ | 4$f$ electron-based topological Kondo insulators have long been researched
for their potential to conduct electric current via protected surface states,
while simultaneously exhibiting unusually robust insulating behavior in their
interiors. To this end, we have investigated the electrical transport of the
3$d$-based correlated insulators FeSi and FeSb$_2$, which have exhibited enough
similarities to their $f$ electron cousins to warrant investigation. By using a
double-sided Corbino disk transport geometry, we show unambiguous evidence of
surface conductance in both of these Fe-based materials. In addition, by using
a 4-terminal Corbino inverted resistance technique, we extract the bulk
resistivity as a function of temperature. Similar to topological Kondo
insulator SmB$_6$, the bulk resistivity of FeSi and FeSb$_2$ are confirmed to
exponentially increase by up to 9 orders of magnitude from room temperature to
the lowest accessible temperature. This demonstrates that these materials are
excellent bulk insulators, providing an ideal platform for studying correlated
2D physics. | 2302.09996v1 |
2023-06-27 | Phase transitions associated with magnetic-field induced topological orbital momenta in a non-collinear antiferromagnet | Resistivity measurements are widely exploited to uncover electronic
excitations and phase transitions in metallic solids. While single crystals are
preferably studied to explore crystalline anisotropies, these usually cancel
out in polycrystalline materials. Here we show that in polycrystalline
Mn3Zn0.5Ge0.5N with non-collinear antiferromagnetic order, changes in the
diagonal and, rather unexpected, off-diagonal components of the resistivity
tensor occur at low temperatures indicating subtle transitions between magnetic
phases of different symmetry. This is supported by neutron scattering and
explained within a phenomenological model which suggests that the phase
transitions in magnetic field are associated with field induced topological
orbital momenta. The fact that we observe transitions between spin phases in a
polycrystal, where effects of crystalline anisotropy are cancelled suggests
that they are only controlled by exchange interactions. The observation of an
off-diagonal resistivity extends the possibilities for realising
antiferromagnetic spintronics with polycrystalline materials. | 2306.15332v1 |
2023-10-20 | 3D Printed Architectured Silicones with Autonomic Self-healing and Creep-resistant Behavior | Self-healing silicones that are able to restore the functionalities and
extend the lifetime of soft devices hold great potential in many applications.
However, currently available silicones need to be triggered to self-heal or
suffer from creep-induced irreversible deformation during use. Here, we design
and print silicone objects that are programmed at the molecular and
architecture levels to achieve self-healing at room temperature while
simultaneously resisting creep. At the molecular scale, dioxaborolanes moieties
are incorporated into silicones to synthesize self-healing vitrimers, whereas
conventional covalent bonds are exploited to make creep-resistant elastomers.
When combined into architectured printed parts at a coarser length scale,
layered materials exhibit fast healing at room temperature without compromising
the elastic recovery obtained from covalent polymer networks. A
patient-specific vascular phantom is printed to demonstrate the potential of
architectured silicones in creating damage-resilient functional devices using
molecularly designed elastomer materials. | 2311.05633v1 |
2024-04-30 | Evaluation of Thermal Performance of a Wick-free Vapor Chamber in Power Electronics Cooling | Efficient thermal management in high-power electronics cooling can be
achieved using phase-change heat transfer devices, such as vapor chambers.
Traditional vapor chambers use wicks to transport condensate for efficient
thermal exchange and to prevent "dry-out" of the evaporator. However, wicks in
vapor chambers present significant design challenges arising out of large
pressure drops across the wicking material, which slows down condensate
transport rates and increases the chances for dry-out. Thicker wicks add to
overall thermal resistance, while deterring the development of thinner devices
by limiting the total thickness of the vapor chamber. Wickless vapor chambers
eliminate the use of metal wicks entirely, by incorporating complementary
wettability-patterned flat plates on both the evaporator and the condenser
side. Such surface modifications enhance fluid transport on the evaporator
side, while allowing the chambers to be virtually as thin as imaginable,
thereby permitting design of thermally efficient thin electronic cooling
devices. While wick-free vapor chambers have been studied and efficient design
strategies have been suggested, we delve into real-life applications of
wick-free vapor chambers in forced air cooling of high-power electronics. An
experimental setup is developed wherein two Si-based MOSFETs of TO-247-3
packaging having high conduction resistance, are connected in parallel and
switched at 100 kHz, to emulate high frequency power electronics operations. A
rectangular copper wick-free vapor chamber spreads heat laterally over a
surface 13 times larger than the heating area. This chamber is cooled
externally by a fan that circulates air at room temperature. The present
experimental setup extends our previous work on wick-free vapor chambers, while
demonstrating the effectiveness of low-cost air cooling in vapor-chamber
enhanced high-power electronics applications. | 2404.19195v1 |
2017-07-26 | Particle acceleration with anomalous pitch angle scattering in 2D MHD reconnection simulations | The conversion of magnetic energy into other forms during solar flares is one
of the outstanding open problems in solar physics. It is generally accepted
that magnetic reconnection plays a crucial role in these conversion processes.
To achieve the rapid energy release required in solar flares, an anomalous
resistivity, orders of magnitude higher than the Spitzer resistivity, is often
used in MHD simulations of reconnection. Spitzer resistivity is based on
Coulomb scattering, which becomes negligible at the high energies achieved by
accelerated particles. As a result, simulations of particle acceleration in
reconnection events are often performed in the absence of any interaction
between accelerated particles and any background plasma. This need not be the
case for scattering associated with anomalous resistivity caused by turbulence
within solar flares, as the higher resistivity implies an elevated scattering
rate. We present results of test particle calculations, with and without pitch
angle scattering, subject to fields derived from MHD simulations of
two-dimensional (2D) X-point reconnection. Scattering rates proportional to the
ratio of the anomalous resistivity to the local Spitzer resistivity, as well as
at fixed values, are considered. Pitch angle scattering, which is independent
of the anomalous resistivity, causes higher maximum energies in comparison to
those obtained without scattering. Scattering rates which are dependent on the
local anomalous resistivity tend to produce fewer highly energised particles
due to weaker scattering in the separatrices, even though scattering in the
current sheet may be stronger when compared to resistivity-independent
scattering. Strong scattering also causes an increase in the number of
particles exiting the computational box in the reconnection outflow region, as
opposed to along the separatrices as is the case in the absence of scattering. | 1709.00305v1 |
2023-02-04 | Smooth, homogeneous, high-purity Nb3Sn superconducting RF resonant cavity by seed-free electrochemical synthesis | Workbench-size particle accelerators, enabled by Nb3Sn-based superconducting
radio-frequency (SRF) cavities, hold the potential of driving scientific
discovery by offering a widely accessible and affordable source of high-energy
electrons and X-rays. Thin-film Nb3Sn RF superconductors with high quality
factors, high operation temperatures, and high-field potentials are critical
for these devices. However, surface roughness, non-stoichiometry, and
impurities in Nb3Sn deposited by conventional Sn-vapor diffusion prevent them
from reaching their theoretical capabilities. Here we demonstrate a seed-free
electrochemical synthesis that pushes the limit of chemical and physical
properties in Nb3Sn. Utilization of electrochemical Sn pre-deposits reduces the
roughness of converted Nb3Sn by five times compared to typical vapor-diffused
Nb3Sn. Quantitative mappings using chemical and atomic probes confirm improved
stoichiometry and minimized impurity concentrations in electrochemically
synthesized Nb3Sn. We have successfully applied this Nb3Sn to the large-scale
1.3 GHz SRF cavity and demonstrated ultra-low BCS surface resistances at
multiple operation temperatures, notably lower than vapor-diffused cavities.
Our smooth, homogeneous, high-purity Nb3Sn provides the route toward high
efficiency and high fields for SRF applications under helium-free cryogenic
operations. | 2302.02054v2 |
2018-03-08 | Design of a nickel-base superalloy using a neural network | A new computational tool has been developed to model, discover, and optimize
new alloys that simultaneously satisfy up to eleven physical criteria. An
artificial neural network is trained from pre-existing materials data that
enables the prediction of individual material properties both as a function of
composition and heat treatment routine, which allows it to optimize the
material properties to search for the material with properties most likely to
exceed a target criteria. We design a new polycrystalline nickel-base
superalloy with the optimal combination of cost, density, gamma' phase content
and solvus, phase stability, fatigue life, yield stress, ultimate tensile
strength, stress rupture, oxidation resistance, and tensile elongation.
Experimental data demonstrates that the proposed alloy fulfills the
computational predictions, possessing multiple physical properties,
particularly oxidation resistance and yield stress, that exceed existing
commercially available alloys. | 1803.03039v1 |
2023-04-22 | Studies of two-dimensional material resistive random-access memory by kinetic Monte Carlo simulations | Resistive memory based on 2D WS2, MoS2, and h-BN materials has been studied,
including experiments and simulations. The influences with different active
layer thicknesses have been discussed, including experiments and simulations.
The thickness with the best On/Off ratio is also found for the 2D RRAM. This
work reveals fundamental differences between a 2D RRAM and a conventional oxide
RRAM. Furthermore, from the physical parameters extracted with the KMC model,
the 2D materials have a lower diffusion activation energy from the vertical
direction, where a smaller bias voltage and a shorter switching time can be
achieved. It was also found the diffusion activation energy from the CVD-grown
sample is much lower than the mechanical exfoliated sample. The result shows
MoS2 has the fastest switching speed among three 2D materials. | 2304.11345v2 |
2018-11-25 | Atomic mechanisms of fast diffusion of large atoms in Germanium | The performance of strained silicon as the channel material for transistors
has plateaued. Motivated by increasing charge-carrier mobility within the
device channel to improve transistor performance, germanium (Ge) is considered
as an attractive option as a silicon replacement due to its highest p-type
mobility in all of the known semiconductor materials and being compatible with
today's conventional CMOS manufacturing process. However, the intrinsically
high carrier mobility of Ge becomes significantly degraded because Ge's native
oxide is unstable and readily decomposes into several GexOy suboxides with a
high density of dangling bonds at the surface. In addition, these interface
trap states will also degrade the off-state leakage current and subthreshold
turn-off of a Ge-based device, significantly affecting its stability.
Furthermore, obtaining low-resistance Ohmic contacts to n-type Ge is another
key challenge in developing Ge CMOS. To solve these challenges, extensive
efforts have been made about the incorporation of new materials, such as Al2O3,
SiN3, TiO2, ZnO, Ge3N4, MgO, HfO2, SrTiO3, and Y2O3, into Ge transistors.
Controlling the diffusion of foreign atoms into Ge is therefore a critical
issue in developing Ge transistors regarding that foreign impurities may be
detrimental to devices. In this work, we study the diffusion properties of all
common elements in Ge by performing the first-principle calculations with a
nudged elastic band method. We find some large atoms, such as Cu, Au, Pd, etc.,
have a very small diffusion barrier. We reveal the underlying mechanism in a
combination of local distortion induced by size effect and bonding effect that
controls the diffusion behaviors of different atoms in Ge. This comprehensive
study and relatively in-depth understanding of diffusion in Ge provides us with
a practical guide for utilizing it more efficiently in semiconductor devices. | 1811.10046v1 |
2022-07-29 | Reactive Two-Step Additive Manufacturing of Ultra-high Temperature Carbide Ceramics | Ultra-high-temperature ceramics (UHTCs) are candidate structural materials
for applications that require resiliency to extreme temperature (>2000{\deg}C),
high mechanical loads, or aggressive oxidizing environments. Processing UHTC
transition metal carbides as standalone materials using additive manufacturing
(AM) methods has not been fully realized due to their extremely slow atomic
diffusivities that impede sintering and large volume changes during indirect AM
that can induce defect structures. In this work, a two-step, reactive AM
approach was studied for the formation of the ultra-high temperature ceramic
TiCx. Readily available equipment including a polymer powder bed fusion AM
machine and a traditional tube furnace were used to produce UHTC cubes and
lattice structures with sub-millimeter resolution. This processing scheme
incorporated, (1) selective laser sintering of a Ti precursor mixed with a
phenolic binder for green body shaping, and (2) ex-situ, isothermal gas-solid
conversion of the green body in CH4 to form TiCx structures. Reactive
post-processing in CH4 resulted in up to 98.2 wt% TiC0.90 product yield and a
reduction in net-shrinkage during consolidation due to the volume expansion
associated with the conversion of Ti to TiC. Results indicated that reaction
bonding associated with the Gibbs free energy release associated with TiC
formation produced interparticle adhesion at low furnace processing
temperatures. The ability to bond highly refractory materials through this type
of process resulted in structures that were crack-free and resisted fracture
during thermal shock testing. Broadly, the additive manufacturing approach
presented could be useful for the production of many UHTC carbides that might
otherwise be incompatible with prevailing AM techniques that do not include
reaction synthesis. | 2208.00052v3 |
2003-05-29 | Structural and electrical properties of tantalum nitride thin films fabricated by using reactive radio-frequency magnetron sputtering | TaN thin film is an attractive interlayer as well as a diffusion barrier
layer in [FeN/TaN](n) multilayers for the application as potential write-head
materials in high-density magnetic recording. We synthesized two series of TaN
films on glass and Si substrates by using reactive radio-frequency sputtering
under 5-mtorr Ar/N-2 processing pressure with varied N-2 partial pressure, and
carried out systematic characterization analyses of the films. We observed
clear changes of phases in the films from metallic bcc Ta to a mixture of bcc
Ta(N) and hexagonal Ta2N, then sequentially to fcc TaN and a mixture of TaN
with N-rich phases when the N2 partial pressure increased from 0.0% to 30%. The
changes were associated with changes in the grain shapes as well as in the
preferred crystalline orientation of the films from bcc Ta [100] to [110], then
to random and finally to fcc TaN [111], correspondingly. They were also
associated with a change in film resistivity from metallic to
semiconductor-like behavior in the range of 77-295 K. The films showed a
typical polycrystalline textured structure with small, crystallized domains and
irregular grain shapes. Clear preferred (111) stacks parallel to the substrate
surface with embedded amorphous regions were observed in the film. TaN film
with [ 111]-preferred orientation and a resistivity of 6.0 m Omega cm was
obtained at 25% N-2 partial pressure, which may be suitable for the interlayer
in [FeN/TaN](n) multilayers. | 0305683v2 |
2011-12-08 | Structural, Thermal, Magnetic and Electronic Transport Properties of the LaNi2(Ge{1-x}P{x})2 System | Polycrystalline samples of LaNi2(Ge{1-x}P{x})2 (x = 0, 0.25, 0.50, 0.75, 1)
were synthesized and their properties investigated by x-ray diffraction (XRD),
heat capacity Cp, magnetic susceptibility chi, and electrical resistivity rho
measurements versus temperature T. These compounds all crystallize in the
body-centered-tetragonal ThCr2Si2-type structure. The rho(T) measurements
indicate that all compositions in this system are metallic. The low-T Cp
measurements yield a rather large Sommerfeld coefficient gamma = 12.4(2) mJ/mol
K^2 for x = 0 reflecting a large density of states at the Fermi energy that is
comparable with the largest values found for the AFe2As2 class of materials
with the same crystal structure. The gamma decreases approximately linearly
with x to 7.4(1) mJ/mol K^2 for x = 1. The chi measurements show nearly
temperature-independent paramagnetic behavior across the entire range of
compositions except for LaNi2Ge2, where a broad peak is observed at 300 K from
chi(T) measurements up to 1000 K that may arise from short-range
antiferromagnetic correlations in a quasi-two-dimensional magnetic system.
High-accuracy Pade approximants representing the Debye lattice heat capacity
and Bloch-Gruneisen electron-phonon resistivity functions versus T are
presented and are used to analyze our experimental Cp(T) and rho(T) data,
respectively. The T-dependences of rho for all samples are well-described by
the Bloch-Gruneisen model, although the observed rho(300 K) values are larger
than calculated from this model. A significant T-dependence of the Debye
temperature determined from the Cp(T) data was observed for each composition.
No clear evidence for bulk superconductivity or any other long-range phase
transition was found for any of the compositions studied. | 1112.1864v2 |
2013-08-14 | Stable pseudoanalytical computation of electromagnetic fields from arbitrarily-oriented dipoles in cylindrically stratified media | Computation of electromagnetic fields due to point sources (Hertzian dipoles)
in cylindrically stratified media is a classical problem for which analytical
expressions of the associated tensor Green's function have been long known.
However, under finite-precision arithmetic, direct numerical computations based
on the application of such analytical (canonical) expressions invariably lead
to underflow and overflow problems related to the poor scaling of the
eigenfunctions (cylindrical Bessel and Hankel functions) for extreme arguments
and/or high-order, as well as convergence problems related to the numerical
integration over the spectral wavenumber and to the truncation of the infinite
series over the azimuth mode number. These problems are exacerbated when a
disparate range of values is to be considered for the layers' thicknesses and
material properties (resistivities, permittivities, and permeabilities), the
transverse and longitudinal distances between source and observation points, as
well as the source frequency. To overcome these challenges in a systematic
fashion, we introduce herein different sets of range-conditioned, modified
cylindrical functions (in lieu of standard cylindrical eigenfunctions), each
associated with non-overlapped subdomains of (numerical) evaluation to allow
for stable computations under any range of physical parameters. In addition
adaptively-chosen integration contours are employed in the complex spectral
wavenumber plane to ensure convergent numerical integration in all cases. We
illustrate the application of the algorithm to problems of geophysical interest
involving layer resistivities ranging from 1000 $\Omega \cdot$m to 10$^{-8}
\Omega \cdot$m, frequencies of operation ranging from 10 MHz down to the low
magnetotelluric range of 0.01 Hz, and for various combinations of layer
thicknesses. | 1308.3179v2 |
2019-03-01 | Coexistence of metallic and nonmetallic properties in the pyrochlore Lu$_2$Rh$_2$O$_7$ | Transition metal oxides of the $4d$ and $5d$ block have recently become the
targets of materials discovery, largely due to their strong spin-orbit coupling
that can generate exotic magnetic and electronic states. Here we report the
high pressure synthesis of Lu$_2$Rh$_2$O$_7$, a new cubic pyrochlore oxide
based on $4d^5$ Rh$^{4+}$ and characterizations via thermodynamic, electrical
transport, and muon spin relaxation measurements. Magnetic susceptibility
measurements reveal a large temperature-independent Pauli paramagnetic
contribution, while heat capacity shows an enhanced Sommerfeld coefficient,
$\gamma$ = 21.8(1) mJ/mol-Rh K$^2$. Muon spin relaxation measurements confirm
that Lu$_2$Rh$_2$O$_7$ remains paramagnetic down to 2 K. Taken in combination,
these three measurements suggest that Lu$_2$Rh$_2$O$_7$ is a correlated
paramagnetic metal with a Wilson ratio of $R_W = 2.5$. However, electric
transport measurements present a striking contradiction as the resistivity of
Lu$_2$Rh$_2$O$_7$ is observed to monotonically increase with decreasing
temperature, indicative of a nonmetallic state. Furthermore, although the
magnitude of the resistivity is that of a semiconductor, the temperature
dependence does not obey any conventional form. Thus, we propose that
Lu$_2$Rh$_2$O$_7$ may belong to the same novel class of non-Fermi liquids as
the nonmetallic metal FeCrAs. | 1903.00399v1 |
2022-01-10 | Alloyed B-(AlxGa1-x)2O3 bulk Czochralski single B-(Al0.1Ga0.9)2O3 and polycrystals B-(Al0.33Ga0.66)2O3, B-(Al0.5Ga0.5)2O3), and property trends | In this work, bulk Czochralski-grown single crystals of 10 mol. % Al2O3
alloyed B-Ga2O3 - monoclinic 10% AGO or B-(Al0.1Ga0.9)2O3 - are obtained, which
show +0.20 eV increase in the bandgap compared with unintentionally doped
B-Ga2O3. Further, growths of 33% AGO - B-(Al0.33Ga0.67)2O3 - and 50% AGO -
B-(Al0.5Ga0.5)2O3 or B-AlGaO3 - produce polycrystalline single-phase monoclinic
material (B-AGO). All three compositions are investigated by x-ray diffraction,
Raman spectroscopy, optical absorption, and 27Al nuclear magnetic resonance
(NMR). By investigating single phase B-AGO over a large range of Al2O3
concentrations (10 - 50 mol. %), broad trends in the lattice parameter,
vibrational modes, optical bandgap, and crystallographic site preference are
determined. All lattice parameters show a linear trend with Al incorporation.
According to NMR, aluminum incorporates on both crystallographic sites of
B-Ga2O3, with a slight preference for the octahedral (GaII) site, which becomes
more disordered with increasing Al. Single crystals of 10% AGO were also
characterized by x-ray rocking curve, transmission electron microscopy, purity
(glow discharge mass spectroscopy and x-ray fluorescence), optical transmission
(200 nm - 20 um wavelengths), and resistivity. These measurements suggest that
electrical compensation by impurity acceptor doping is not the likely
explanation for high resistivity, but rather the shift of a hydrogen level from
a shallow donor to a deep acceptor due to Al alloying. .. Cont.
This article may be downloaded for personal use only. Any other use requires
prior permission of the author and AIP Publishing. This article appeared in
Journal of Applied Physics 131 155702. | 2201.03673v2 |
2023-02-09 | Spark Discharge Generator as a Stable and Reliable Nanoparticle Synthesis Device: Analysis of the Impact of Process and Circuit Variables on the Characteristics of Synthesized Nanoparticles | Nanotechnology offers the promise of harnessing quantum properties not
available in the bulk phase. These desirable properties are highly dependent on
size and composition. Generators that control these variables are therefore
essential for progress in the field. The spark discharge generator (SDG) is an
outstanding aerosol route for nanoparticle synthesis, which stands out due to
its fast kinetics, scalability, high purity, accuracy and reproducibility with
the added advantage of allowing the synthesis of nanoparticles of any
conducting material. These advantages are a consequence of its vast heating and
cooling rates, its intrinsic and easily controllable electronic variables at
the reach of a click. However, the mechanistic impact of these variables on the
actual aerosol generated is still not fully understood. In this work, we
constructed an SDG and systematically studied its behavior with particular
interest in the effect that resistance, capacitance, inductance, flow rate, gap
separation and current have on the electrical behavior of the spark. Our model
system produced primarily Fe and Cu nanoparticles with measured concentrations.
We discuss how the spark influences particle size and number concentration and
provide useful correlations that link dependent with independent variables.
Remarkably, a finite resistance produces a maximum in the output of the
generated aerosols. This suggests a direct link between RLC properties of the
circuit and cabling into the frequency of the spark, and nanoparticle number
concentration, indicating potential for exploiting such behavior towards
maximizing nanoparticle generation. Furthermore, we discuss a link between
spark oscillations and energy release with its consequent aerosol generation. | 2302.04760v1 |
2013-08-08 | Ultra-low Energy, High-Performance Dynamic Resistive Threshold Logic | We propose dynamic resistive threshold-logic (DRTL) design based on
non-volatile resistive memory. A threshold logic gate (TLG) performs summation
of multiple inputs multiplied by a fixed set of weights and compares the sum
with a threshold. DRTL employs resistive memory elements to implement the
weights and the thresholds, while a compact dynamic CMOS latch is used for the
comparison operation. The resulting DRTL gate acts as a low-power, configurable
dynamic logic unit and can be used to build fully pipelined, high-performance
programmable computing blocks. Multiple stages in such a DRTL design can be
connected using energy-efficient low swing programmable interconnect networks
based on resistive switches. Owing to memory-based compact logic and
interconnect design and highspeed dynamic-pipelined operation, DRTL can achieve
more than two orders of magnitude improvement in energy-delay product as
compared to look-up table based CMOS FPGA. | 1308.4672v1 |
2013-10-11 | Curvature dependence of the interfacial heat and mass transfer coefficients | Nucleation is often accompanied by heat transfer between the surroundings and
a nucleus of a new phase. The interface between two phases gives an additional
resistance to this transfer. For small nuclei the interfacial curvature is
high, which affects not only equilibrium quantities such as surface tension,
but also the transport properties. In particular, high curvature affects the
interfacial resistance to heat and mass transfer. We develop a framework for
determining the curvature dependence of the interfacial heat and mass transfer
resistances. We determine the interfacial resistances as a function of a
curvature. The analysis is performed for a bubble of a one-component fluid and
may be extended to various nuclei of multicomponent systems. The curvature
dependence of the interfacial resistances is important in modeling transport
processes in multiphase systems. | 1310.3025v1 |
2014-08-30 | Anisotropic resistivity of the monolayer graphene in the trigonal warping and connected Fermi curve regimes | In the present study, the anisotropic resistivity of the monolayer graphene
has been obtained in semiclassical regime beyond the Dirac point approximation.
In particular, detailed investigations were made on the dependence of
conductivity on the Fermi energy. At low energies, in the vicinity of the Dirac
points, band energy of the monolayer graphene is isotropic at the Fermi level.
Meanwhile, at the intermediate Fermi energies anisotropic effects such as
trigonal warping is expected to be the origin of the anisotropic resistivity.
However, besides the band anisotropy there also exists an other source of
anisotropic resistivity which was introduced by scattering matrix. At high
energies it was shown that the band anisotropy is less effective than the
anisotropy generated by the scattering matrix. It was also shown that there
exist two distinct regimes of anisotropic resistivity corresponding the
trigonal warping and connected Fermi curve at intermediate and high energies
respectively. | 1409.0130v1 |
2018-08-19 | Temperature Dependence of In-plane Resistivity and Inverse Hall Angle in NLED Holographic Model | In the strange metal phase of the high-$T_{c}$ cuprates, it is challenging to
explain the linear temperature dependence of the in-plane resistivity and the
quadratic temperature dependence of the inverse Hall angle. In this paper, we
investigate the temperature dependence of the in-plane resistivity and inverse
Hall angle in the nonlinear electrodynamics holographic model developed in our
recent work. Maxwell electrodynamics and Born-Infeld electrodynamics are
considered. Both cases support a wide spectrum of temperature scalings in
parameter space. For Maxwell electrodynamics, the T-linear in-plane resistivity
generally dominates at low temperatures and survives into higher temperatures
in a narrow strip-like manner. Meanwhile, the T-quadratic inverse Hall angle
dominates at high temperatures and extends down to lower temperatures. The
overlap between the T-linear in-plane resistivity and the T-quadratic inverse
Hall angle, if occurs, would generally present in the intermediate temperate
regime. The Born-Infeld case with $a>0$ is quite similar to the Maxwell case.
For the Born-Infeld case with $a<0$, there can be a constraint on the charge
density and magnetic field. Moreover, the overlap can occur for strong charge
density. | 1808.06158v1 |
2019-04-18 | Non-Stationary Polar Codes for Resistive Memories | Resistive memories are considered a promising memory technology enabling high
storage densities with in-memory computing capabilities. However, the readout
reliability of resistive memories is impaired due to the inevitable existence
of wire resistance, resulting in the sneak path problem. Motivated by this
problem, we study polar coding over channels with different reliability levels,
termed non-stationary polar codes, and we propose a technique improving its bit
error rate (BER) performance. We then apply the framework of non-stationary
polar codes to the crossbar array and evaluate its BER performance under two
modeling approaches, namely binary symmetric channels (BSCs) and binary
asymmetric channels (BSCs). Finally, we propose a technique for biasing the
proportion of high-resistance states in the crossbar array and show its
advantage in reducing further the BER. Several simulations are carried out
using a SPICE-like simulator, exhibiting significant reduction in BER. | 1904.08966v1 |
2019-12-06 | Write and Read Channel Models for 1S1R Crossbar Resistive Memory with High Line Resistance | Crossbar resistive memory with 1 Selector 1 Resistor (1S1R) structure is
attractive for low-cost and high-density nonvolatile memory applications. As
technology scales down to the single-nm regime, the increasing resistivity of
wordline/bitline becomes a limiting factor to device reliability. This paper
presents write/read communication channels while considering the line
resistance and device variabilities by statistically relating the degraded
write/read margins and the channel parameters. Binary asymmetric channel (BAC)
models are proposed for the write/read operations. Simulations based on these
models suggest that the bit-error rate of devices are highly non-uniform across
the memory array. These models provide quantitative tools for evaluating the
trade-offs between memory reliability and design parameters, such as array
size, technology nodes, and aspect ratio, and also for designing
coding-theoretic solutions that would be most effective for crossbar memory. | 1912.02963v3 |
2020-05-15 | Anomalous Electrical Conduction and Negative Temperature Coefficient of Resistance in Nanostructured Gold Resistive Switching Films | We report on the observation of non-metallic electrical conduction, resistive
switching, and a negative temperature coefficient of resistance in
cluster-assembled nanostructured gold films above the electrical percolation
and in strong-coupling regime, from room to cryogenic temperatures (24K). The
structure of the films is characterized by an extremely high density of
randomly oriented crystalline nanodomains, separated by grain boundaries. The
observed behavior can be explained by considering space charge limited
conduction and Coulomb blockade phenomena highlighting the influence of the
high density of defects and grain boundaries on the localization of conduction
electrons. Our findings have implications for a broad class of resistive
switching systems based on random assemblies of nanoobjects. | 2005.07401v1 |
2021-05-22 | Dynamic-quenching of a single-photon avalanche photodetector using an adaptive resistive switch | One of the most common approaches for quenching single-photon avalanche
diodes is to use a passive resistor in series with it. A drawback of this
approach has been the limited recovery speed of the single-photon avalanche
diodes. High resistance is needed to quench the avalanche, leading to slower
recharging of the single-photon avalanche diodes depletion capacitor. We
address this issue by replacing a fixed quenching resistor with a
bias-dependent adaptive resistive switch. Reversible generation of metallic
conduction enables switching between low and high resistance states under
unipolar bias. As an example, using a Pt/Al2O3/Ag resistor with a commercial
silicon single-photon avalanche diodes, we demonstrate avalanche pulse widths
as small as ~30 ns, 10x smaller than a passively quenched approach, thus
significantly improving the single-photon avalanche diodes frequency response.
The experimental results are consistent with a model where the adaptive
resistor dynamically changes its resistance during discharging and recharging
the single-photon avalanche diodes. | 2105.11454v2 |
2022-09-14 | Picosecond Time-Scale Resistive Switching Monitored in Real-Time | The resistance state of filamentary memristors can be tuned by relocating
only a few atoms at interatomic distances in the active region of a conducting
filament. Thereby the technology holds promise not only in its ultimate
downscaling potential and energy efficiency but also in unprecedented speed.
Yet, the breakthrough in high-frequency applications still requires the
clarification of the dominant mechanisms and inherent limitations of ultra-fast
resistive switching. Here we investigate bipolar, multilevel resistive
switchings in tantalum pentoxide based memristors with picosecond time
resolution. We experimentally demonstrate cyclic resistive switching operation
due to 20 ps long voltage pulses of alternating polarity. Through the analysis
of the real-time response of the memristor we find that the set switching can
take place at the picosecond time-scale where it is only compromised by the
bandwidth limitations of the experimental setup. In contrast, the completion of
the reset transitions significantly exceeds the duration of the ultra-short
voltage bias, demonstrating the dominant role of thermal diffusion and
underlining the importance of dedicated thermal engineering for future
high-frequency memristor circuit applications. | 2209.06732v1 |
2022-12-02 | Nondestructive KPFM-assisted Quality Control in Fabrication of GaAs High-Speed Electronics | In this paper, we report on the method of nondestructive quality control that
can be used in fabrication of GaAs high-speed electronics. The method relies on
the surface potential mapping and enables rigid in vivo analysis of transport
properties of an active electronic device incorporated into a complex
integrated circuit. The study is inspired by our ongoing development of a
millimeter wave intelligent reflective surface for 6G communications. To
provide desired beamforming capabilities, such a surface should utilize
hundreds of identical microscale GaAs diode switches with series resistance of
a few ohms. Thus, we develop a ladder-like layered ohmic contact to heavily
Si-doped GaAs and cross-study it via transmission line method and Kelvin probe
force microscopy. The contact resistivity as low as 0.15~$\mu \Omega \,$cm$^2$
is measured resulting in only a 0.6~$\Omega$ of resistance for the contact area
of 3$\times$3~$\mu$m$^2$. Moreover, the tendencies observed suggest that one
can rigidly analyze the evolution of contact resistance and the profile of
resistivity under contact in response to rapid thermal annealing, once the
surface potential map across the ``ladder'' is known. | 2212.01474v1 |
2023-09-22 | Terahertz scale microbunching instability driven by nonevaporable getter coating resistive-wall impedance | Non-evaporable getter (NEG) coating is widely required in the next generation
of light sources and circular $e^+e^-$ colliders for small vacuum pipes to
improve the vacuum level, which, however, also enhances the high-frequency
resistive-wall impedance and often generates a resonator-like peak in the
terahertz frequency region. In this paper, we will use the parameters of the
planned Hefei Advanced Light Facility (HALF) storage ring to study the impact
of NEG coating resistive-wall impedance on the longitudinal microwave
instability via particle tracking simulation. Using different NEG coating
parameters (resistivity and thickness) as examples, we find that the impedance
with a narrow and strong peak in the high frequency region can cause
micro-bunching instability, which has a low instability threshold current and
contributes to a large energy spread widening above the threshold. In order to
obtain a convergent simulation of the beam dynamics, one must properly resolve
such a peak. The coating with a lower resistivity has a much less sharp peak in
its impedance spectrum, which is helpful to suppress the micro-bunching
instability and in return contributes to a weaker microwave instability. | 2309.12779v1 |
2024-04-29 | Evolution of secondary electron spectrum during cosmic-ray discharge in the universe | We recently found that streaming cosmic rays (CRs) induce a resistive
electric field that can accelerate secondary electrons produced by CR
ionization. In this work, we study the evolution of the energy spectrum of
secondary electrons by numerically solving the one-dimensional Boltzmann
equation and Ohm's law. We show that the accelerated secondary electrons
further ionize a gas, that is, the electron avalanche occurs, resulting in
increased ionization and excitation of the gas. Although the resistive electric
field becomes weaker than one before the CR discharge, the weak resistive
electric field weakly accelerates the secondary electrons. The quasi-steady
state is almost independent of the initial resistive electric field, but
depends on the electron fraction in the gas. The resistive electric field in
the quasi-steady state is larger for the higher electron fraction, which makes
the number of secondary electrons that can ionize the gas larger, resulting in
a higher ionization rate. The CR discharge could explain the high ionization
rate that are observed in some molecular clouds. | 2404.18513v1 |
2007-03-26 | An alternative normal state c-axis resistivity model for high-Tc superconductors | An alternative model for c-axis resistivity in layered high-Tc crystalline
superconductors is proposed and has been characterized as an essentially
two-dimensional Fermi liquid. Average ionization energy is included as
additional parameter that determines the concentration of tunnelling electrons
between Cu-O2 layers. This model agrees well quantitatively with the Bi2212 and
Y123 single crystals, and qualitatively with the pure 1212 phase polycrystals. | 0703658v1 |
2005-02-02 | Phase transitions in Lu$_2$Ir$_3$Si$_5$ | We report the results of our investigations on a polycrystalline sample of
Lu$_2$Ir$_3$Si$_5$ which crystallizes in the U$_2$Co$_3$Si$_5$ type structure
(Ibam). These investigations comprise powder X-ray diffraction, magnetic
susceptibility, electrical resistivity and high temperature (120-300 K) heat
capacity studies. Our results reveal that the sample undergoes a
superconducting transition below 3.5 K. It also undergoes a first order phase
transition between 150-250 K as revealed by an upturn in the resistivity, a
diasmagnetic drop in the magnetic susceptibility and a large anomaly (20-30
J/mol K) in the specific heat data. We observe a huge thermal hysteresis of
almost 45 K between the cooling and warming data across this high temperature
transition in all our measurements. Low temperature X-ray diffraction
measurements at 87 K reveals that the compound undergoes a structural change at
the high temperature transition. Resistivity data taken in repeated cooling and
warming cycles indicate that at the high temperature transition, the system
goes into a highly metastable state and successive heating/cooling curves are
found to lie above the previous one and the resistance keeps increasing with
every thermal cycle. The room temperature resistance of a thermaly cycled piece
of the sample decays exponentialy with time with a decay time constant
estimated to be about 10$^4$ secs. The anomaly (upturn) in the resistivity and
the large drop (almost 45%) in the susceptibility across the high temperature
transition suggest that the observed structural change is accompanied or
induced by an electronic transition. | 0502041v2 |
2014-06-23 | Resistance of helical edges formed in a semiconductor heterostructure | Time-reversal symmetry prohibits elastic backscattering of electrons
propagating within a helical edge of a two-dimensional topological insulator.
However, small band gaps in these systems make them sensitive to doping
disorder, which may lead to the formation of electron and hole puddles. Such a
puddle -- a quantum dot -- tunnel-coupled to the edge may significantly enhance
the inelastic backscattering rate, due to the long dwelling time of an electron
in the dot. The added resistance is especially strong for dots carrying an odd
number of electrons, due to the Kondo effect. For the same reason, the
temperature dependence of the added resistance becomes rather weak. We present
a detailed theory of the quantum dot effect on the helical edge resistance. It
allows us to make specific predictions for possible future experiments with
artificially prepared dots in topological insulators. It also provides a
qualitative explanation of the resistance fluctuations observed in short HgTe
quantum wells. In addition to the single-dot theory, we develop a statistical
description of the helical edge resistivity introduced by random charge puddles
in a long heterostructure carrying helical edge states. The presence of charge
puddles in long samples may explain the observed coexistence of a high sample
resistance with the propagation of electrons along the sample edges. | 1406.6052v2 |
2016-08-03 | Non-Fermi liquid behavior of electrical resistivity close to the nematic critical point in Fe$_{1-x}$Co$_x$Se and FeSe$_{1-y}$S$_y$ | Temperature dependence of resistivity of single crystals of
Fe$_{1-x}$Co$_x$Se and FeSe$_{1-y}$S$_y$ is studied in detail under zero and
high magnetic field (magnetoresistance), the latter of which enables to monitor
the temperature ($T$) evolution of resistivity below the onset of
superconducting transition temperature ($T_{\rm c}$). In FeSe$_{1-y}$S$_y$,
$T$-linear dependence of resistivity is prominent in $y$ = 0.160 below 40 K,
whereas it changes to a Fermi-liquid(FL)-like $T^2$ one below 10 K in $y$ =
0.212. These suggest that the quantum critical point (QCP) originating from the
electronic nematicity resides around $y$ = 0.160 and the fluctuation in QCP
gives rise anomalous $T$-linear dependence in resistivity in a wide $T$ range.
In Fe$_{1-x}$Co$_x$Se, resistivity gradually changes from linear- to quadratic-
$T$-dependent one at low temperatures in the range between $x$ = 0.036 and
0.075. These could be interpreted by scenarios of both the nematic QCP and the
crossover in the ground states between the orthorhombic nematic phase and the
tetragonal phase. The anomalies found as $T$-linear resistivity are discussed
in terms of orbital and spin fluctuation arising from the nematic QCP. | 1608.01044v1 |
2017-08-01 | Heterogeneous Memristive Devices Enabled by Magnetic Tunnel Junction Nanopillars Surrounded by Resistive Silicon Switches | Emerging non-volatile memories (NVMs) have currently attracted great interest
for their potential applications in advanced low-power information storage and
processing technologies. Conventional NVMs, such as magnetic random access
memory (MRAM) and resistive random access memory (RRAM) suffer from limitations
of low tunnel magnetoresistance (TMR), low access speed or finite endurance.
NVMs with synergetic advantages are still highly desired for future computer
architectures. Here, we report a heterogeneous memristive device composed of a
magnetic tunnel junction (MTJ) nanopillar surrounded by resistive silicon
switches, named resistively enhanced MTJ (Re-MTJ), that may be utilized for
novel memristive memories, enabling new functionalities that are inaccessible
for conventional NVMs. The Re-MTJ device features a high ON/OFF ratio of >1000%
and multilevel resistance behaviour by combining magnetic switching together
with resistive switching mechanisms. The magnetic switching originates from the
MTJ, while the resistive switching is induced by a point-switching filament
process that is related to the mobile oxygen ions. Microscopic evidence of
silicon aggregated as nanocrystals along the edges of the nanopillars verifies
the synergetic mechanism of the heterogeneous memristive device. This device
may provide new possibilities for advanced memristive memory and computing
architectures, e.g., in-memory computing and neuromorphics. | 1708.00372v2 |
2021-11-11 | Imaging Hydrodynamic Electrons Flowing Without Landauer-Sharvin Resistance | Electrical resistance usually originates from lattice imperfections. However,
even a perfect lattice has a fundamental resistance limit, given by the
Landauer conductance caused by a finite number of propagating electron modes.
This resistance, shown by Sharvin to appear at the contacts of electronic
devices, sets the ultimate conductance limit of non-interacting electrons.
Recent years have seen growing evidence of hydrodynamic electronic phenomena,
prompting recent theories to ask whether an electronic fluid can radically
break the fundamental Landauer-Sharvin limit. Here, we use single-electron
transistor imaging of electronic flow in high-mobility graphene Corbino disk
devices to answer this question. First, by imaging ballistic flows at
liquid-helium temperatures, we observe a Landauer-Sharvin resistance that does
not appear at the contacts but is instead distributed throughout the bulk. This
underpins the phase-space origin of this resistance - as emerging from spatial
gradients in the number of conduction modes. At elevated temperatures, by
identifying and accounting for electron-phonon scattering, we reveal the
details of the purely hydrodynamic flow. Strikingly, we find that electron
hydrodynamics eliminates the bulk Landuer-Sharvin resistance. Finally, by
imaging spiraling magneto-hydrodynamic Corbino flows, we reveal the key
emergent length scale predicted by hydrodynamic theories - the Gurzhi length.
These observations demonstrate that electronic fluids can dramatically
transcend the fundamental limitations of ballistic electrons, with important
implications for fundamental science and future technologies | 2111.06412v1 |
2022-07-30 | Superconductor relaxation -- A must to be integrated into stability calculations | A superconductor is stable if it does not quench. Quench is a short-time
physics problem. For its deeper understanding of, and how to avoid quench, the
physics behind stability has to be analysed. A previously suggested dynamic
relaxation model is re-considered and applied to YBaCuO 123 and BSCCO 2223
high-temperature, thin film superconductors. Parallel to this investigation, an
unconventional approach using an electrical resistance network (a cell model)
is applied to introduce a method how to estimate the extent by which, in
resistance measurements, exact determination of critical temperature of
superconductors is possible. This resistive cell model, when considering its
numerical convergence behaviour, in a side result may provide an alternative
explanation of (at least a contribution to) bending of resistivity vs.
temperature curves, and perhaps also an alternative to standard explanations of
the thermal fluctuations impact on these curves.
The dynamic relaxation and the resistance models provide a parenthesis that
correlates, in terms of the Ginzburg-Landau order parameter, (i) solution of
superconductor stability problem (the main objective of this paper), with
tentative explanation of (ii) bending of the resistivity curves near critical
temperature and (iii) with predictions from thermal fluctuations. | 2208.00190v4 |
2023-09-25 | Non-Volatile Resistive Switching of Polymer Residues in 2D Material Memristors | Two-dimensional (2D) materials are popular candidates for emerging nanoscale
devices, including memristors. Resistive switching (RS) in such 2D material
memristors has been attributed to the formation and dissolution of conductive
filaments created by the diffusion of metal ions between the electrodes.
However, the area-scalable fabrication of patterned devices involves polymers
that are difficult to remove from the 2D material interfaces without damage.
Remaining polymer residues are often overlooked when interpreting the RS
characteristics of 2D material memristors. Here, we demonstrate that the
parasitic residues themselves can be the origin of RS. We emphasize the
necessity to fabricate appropriate reference structures and employ atomic-scale
material characterization techniques to properly evaluate the potential of 2D
materials as the switching layer in vertical memristors. Our
polymer-residue-based memristors exhibit RS typical for a filamentary mechanism
with metal ion migration, and their performance parameters are strikingly
similar to commonly reported 2D material memristors. This reveals that the
exclusive consideration of electrical data without a thorough verification of
material interfaces can easily lead to misinterpretations about the potential
of 2D materials for memristor applications. | 2309.13900v1 |
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