publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2018-07-18 | 2D Tunnel Field Effect Transistors (FETs) with a Stable Charge-Transfer-Type p$^+$-WSe$_2$ Source | Two-dimensional (2D) materials are highly promising for tunnel field effect
transistors (TFETs) with low subthreshold swing and high drive current because
the shorter tunnel distance and strong gate controllability can be expected
from the van der Waals gap distance and the atomically sharp heterointerface
formed independently of lattice matching. However, the common problem for 2D-2D
TFETs is the lack of highly doped 2D materials with the high process stability
as the sources. In this study, we have found that p+-WSe2 doped by charge
transfer from a WOx surface oxide layer can be stabilized by transferring it
onto a h-BN substrate. Using this p$^+$-WSe$_2$ as a source, we fabricate
all-solid-state 2D-2D heterostructure TFETs with an Al2O3 top gate insulator,
i.e., type-II p$^+$-WSe$_2$ /MoS$_2$ and type-III p$^+$-WSe$_2$ /WSe$_2$. The
band-to-band tunneling and negative differential resistance trends are clearly
demonstrated at low temperatures. This work suggests that high doped 2D crystal
of the charge transfer type is an excellent choice as sources for TFETs. | 1807.06762v1 |
2019-10-14 | Plasmonic Titanium Nitride via Atomic Layer Deposition: A Low-Temperature Route | To integrate plasmonic devices into industry, it is essential to develop
scalable and CMOS compatible plasmonic materials. In this work, we report high
plasmonic quality titanium nitride (TiN) on c-plane sapphire by plasma enhanced
atomic layer deposition (PE-ALD). TiN with low losses and high metallicity was
achieved at temperatures below 500{\deg}C, by exploring the effects of
chemisorption time, substrate temperature and plasma exposure time on material
properties. Reduction in chemisorption time mitigates premature precursor
decomposition at T_S > 375{\deg}C , and a trade-off between reduced impurity
concentration and structural degradation caused by plasma bombardment is
achieved for 25s plasma exposure. 85 nm thick TiN films grown at a substrate
temperature of 450{\deg}C, compatible with CMOS processes, with 0.5s
chemisorption time and 25s plasma exposure exhibited a high plasmonic figure of
merit (|{\epsilon}^'/{\epsilon}^''|) of 2.8 and resistivity of 31
{\mu}{\Omega}-cm. These TiN thin films fabricated with subwavelength apertures
were shown to exhibit extraordinary transmission. | 2001.05063v1 |
2021-06-26 | High Infrared Reflectance Modulation in VO2 Films Synthesized on Glass and ITO coated Glass substrates using Atmospheric Oxidation of Vanadium | Vanadium Dioxide (VO2) is a strongly correlated material, which exhibits
insulator to metal transition at ~68 C along with large resistivity and
infrared optical reflectance modulation. In this work, we use atmospheric
pressure thermal oxidation of Vanadium to synthesize VO2 films on glass and ITO
coated glass substrates. With the optimized short oxidation durations of 2 min
and 4 min, the synthesized VO2 film shows high optical reflectance switching in
long-wavelength infrared on glass substrates and mid-wavelength infrared on ITO
coated glass substrates, respectively. Peak reflectance switching values of
~76% and ~79% are obtained on the respective substrates, which are among the
highest reported values. Using the reflectance data, we extract VO2 complex
refractive index in infrared wavelengths, in both the insulating and metallic
phases. The extracted refractive index shows good agreement with VO2
synthesized using other methods. This demonstration of high optical reflectance
switching in VO2 thin films, grown on low cost glass and ITO coated glass
substrates, using a simple low thermal budget process will aid in enhancing VO2
applications in the optical domain. | 2106.14006v1 |
2022-04-11 | Emergent superconductivity in van der Waals Kagome material Pd3P2S8 under high pressure | Kagome lattice systems have been proposed to host rich physics, which provide
an excellent platform to explore unusual quantum states. Here, we report on the
discovery of superconductivity in van der Waals material Pd3P2S8 under
pressure. The superconductivity is observed in Pd3P2S8 for those pressures
where the temperature dependence of the resistivity changes from a
semiconducting-like behavior to that of a normal metal. The superconducting
transition temperature Tc increases with applied pressure and reaches ~ 6.83 K
at 79.5 GPa. Combining high-pressure XRD, Raman spectroscopy and theoretical
calculations, our results demonstrate that the observed superconductivity
induced by high pressure in Pd3P2S8 is closely related to the formation of
amorphous phase, which results from the structural instability due to the
enhanced coupling between interlayer Pd and S atoms upon compression. | 2204.05179v1 |
2001-07-21 | Distinct origins of magnetic -field -induced resistivity irreversibility in two manganites with similar ground states : Pr$_{0.5}$Sr$_{0.41}$Ca$_{0.09}$MnO$_{3}$ and La$_{0.5}$Ca$_{0.5}$MnO$_{3}$ | Our investigation of the magnetotransport in two charge ordered manganites
with similar magnetic ground states reveals that the origin of
magnetoresistance can not be concluded from the isofield resistivity, $\rho
$(T, constant H), measurements alone. Both
Pr$_{0.5}$Sr$_{0.41}$Ca$_{0.09}$MnO$_{3}$ (PrSrCa) and
La$_{0.5}$Ca$_{0.5}$MnO$_{3}$ (LaCa) show a ferromagnetic transition (T$_{C}$ =
260 K for PrSrCa, 230 K for LaCa) followed by an antiferromagnetic transition
(T$_{N}$ = 170 K for PrSrCa, 140 K for LaCa). These compounds show
qualitatively similar magnetotransport : Below the irreversibility temperature
T$_{IR}$, field cooled (FC) resistivity is lower than zero field cooled (ZFC)
and decreases continuously with T, whereas the ZFC $\rho $(T, H) resembles $\
$the behavior of $\rho $(T, H = 0 T). The value of $\rho $(ZFC)/$\rho $(FC) is
$\approx $ 10$^{4}$ at 5 K and $\mu_{0}$H = 7 T in both compounds. However,
isothermal magnetic measurements suggest distinct origins of magnetoresistance
: Field cooling enhances ferromagnetic phase fraction in LaCa whereas it drives
PrSrCa into a metastable state with high magnetization. The distinct origins of
magnetotransport is also reflected in other magnetic history dependent
properties. | 0107448v1 |
2006-09-15 | Magneto Transport of high TCR (temperature coefficient of resistance) La2/3Ca1/3MnO3: Ag Polycrystalline Composites | We report the synthesis, (micro)structural, magneto-transport and
magnetization of polycrystalline La2/3Ca1/3MnO3:Agx composites with x = 0.0,
0.1, 0.2, 0.3 and 0.4. The temperature coefficient of resistance (TCR) near
ferromagnetic (FM) transition is increased significantly with addition of Ag.
The FM transition temperature (TFM) is also increased slightly with Ag
addition. Magneto-transport measurements revealed that magneto-resistance MR is
found to be maximum near TFM. Further the increased MR of up to 60% is seen
above 300 K for higher silver added samples in an applied field of 7 Tesla.
Sharp TCR is seen near TFM with highest value of up to 15 % for Ag (0.4)
sample, which is an order of magnitude higher than as for present pristine
sample and best value yet reported for any polycrystalline LCMO compound.
Increased TCR, TFM and significant above room temperature MR of
La2/3Ca1/3MnO3:Agx composites is explained on the basis of improved grains size
and connectivity with silver addition in the matrix. Better coupled FM domains
and nearly conducting grain boundaries give rise to improved physical
properties of the La2/3Ca1/3MnO3 manganites. | 0609364v1 |
2007-09-05 | Microwave surface resistance of pristine and neutron-irradiated MgB2 samples in magnetic field | We report on the microwave surface resistance of two polycrystalline Mg11B2
samples; one consists of pristine material, the other has been irradiated at
very high neutron fluence. It has already been reported that in the strongly
irradiated sample the two gaps merge into a single value. The mw surface
resistance has been measured in the linear regime as a function of the
temperature and the DC magnetic field, at increasing and decreasing fields. The
results obtained in the strongly irradiated sample are quite well justified in
the framework of a generalized Coffey and Clem model, in which we take into
account the field distribution inside the sample due to the critical state. The
results obtained in the pristine sample show several anomalies, especially at
low temperatures, which cannot be justified in the framework of standard models
for the fluxon dynamics. Only at temperatures near Tc and for magnetic fields
greater than 0.5Hc2(T) the experimental data can quantitatively be accounted
for by the Coffey and Clem model, provided that the upper-critical-field
anisotropy is taken into due account. | 0709.0618v2 |
2008-02-12 | Two-Fluid Behaviour at the Origin of the Resistivity Peak in Doped Manganites | We report a series of magnetic and transport measurements on high-quality
single crystal samples of colossal magnetoresistive manganites, La_{0.7}
Ca_{0.3} Mn O_3 and Pr_{0.7} Sr_{0.3} Mn O_3. 1 % Fe doping allows a Moessbauer
spectroscopy study, which shows (i) unusual line broadening within the
ferromagnetic phase and (ii) a coexistence of ferro- and paramagnetic
contributions in a region, T_1<T<T_2, around the Curie point T_C. In the case
of Pr_{0.7} Sr_{0.3} Mn O_3, the resistivity peak occurs at a considerably
higher temperature, T_{MI}>T_2. This shows that phase separation into metallic
(ferromagnetic) and insulating (paramagnetic) phases cannot be generally
responsible for the resistivity peak (and hence for the associated colossal
magnetoresistance). Our results can be understood phenomenologically within the
two-fluid approach, which also allows for a difference between T_C and T_{MI}.
Our data indeed imply that while magnetic and transport properties of the
manganites are closely interrelated, the two transitions at T_C and T_{MI} can
be viewed as distinct phenomena. | 0802.1664v3 |
2008-06-15 | Anisotropy in the electrical resistivity and susceptibility of superconducting BaFe$_{2}$As$_{2}$ single crystals | Sizable single crystals of $BaFe_2As_2$ have been grown with self-flux
method. The crystals are plate-like with c-axis perpendicular to the plane. The
size can be as large as 3 x 5 x 0.2 $mm^3$. The resistivity anisotropy
($\rho_c/\rho_{ab}$) is as large as about 150, and independent of temperature.
The transport in ab plane and along c-axis direction shares the same scattering
mechanism. In contrast to the magnetic behavior of polycrystalline samples, no
Curie-Weiss behavior are observed, a temperature linear dependent
susceptibility occurs above spin-density-wave (SDW) transition. The
susceptibility behavior is very similar to that of antiferromagnetic SDW
chromium. Magnetic behavior of single crystal definitely gives evidence for
existence of local moment except for the contribution to susceptibility from
itinerant electrons. A resistivity minimum strongly dependent on magnetic field
is observed. A log(1/T) divergency, similar to that of the underdoped cuprates,
happens at low temperature. Here we first present intrinsic transport and
magnetic properties, and their anisotropy from high quality single crystal. | 0806.2452v2 |
2008-10-01 | Qualitative explanation of the temperature behaviors of the transport properties and magnetic susceptibility of high-temperature superconductors in the normal state | A model based on the alternating structure of the imbedded conduction layers
(the Cu-O2 planes) with the charge-transfer-insulator (CTI) layers is proposed.
There are three kinds of carriers, each with a different behavior:
conduction-like holes in the Cu-O2 layers and electrons and normal holes in the
CTI matrix between the Cu-O2 layers. This structure explains the strong
anisotropies. The relationship is obtained between the concentration nq of
conduction-like holes in the Cu-O2 layers and the temperature T. The anomalous
temperature behavior of the resistivity as well as the Hall constant also
follows. We give the hole density in ab plane a definite physical meaning, and
also define explicitly optimal doping, overdoping and underdoping. Our model
gives the correct temperature dependence of the resistivity and the hole
constant on optimal doping, overdoping and underdoping, and it predicts the
temperature behavior of the cotangent of the Hall angle quite well. Based on
this model, we can also understand that the HiTc materials become "Fermi
Liquids" in the extremely overdoped region, and the dR/dT becomes negative
below some temperature T<1.211T0 in the underdoped case. Based on this model,
the thermal behaviors of the magnetic susceptibility in different doping can
also be easily explained. The resistivity along c-axis is discussed. | 0810.0169v2 |
2011-01-29 | Crystal structure, physical properties and superconductivity in $A_{x}$Fe$_2$Se$_2$ single crystals | We studied the correlation among structure and transport properties and
superconductivity in the different $A_x$Fe$_2$Se$_2$ single crystals ($A$ = K,
Rb, and Cs). Two sets of (00$l$) reflections are observed in the X-ray single
crystal diffraction patterns, and arise from the intrinsic inhomogeneous
distribution of the intercalated alkali atoms. The occurrence of
superconductivity is closely related to the {\sl c}-axis lattice constant, and
the $A$ content is crucial to superconductivity. The hump observed in
resistivity seems to be irrelevant to superconductivity. There exist many
deficiencies within the FeSe layers in $A_x$Fe$_2$Se$_2$, while their $T_{\rm
c}$ does not change so much. In this sense, superconductivity is robust to the
Fe and Se vacancies. Very high resistivity in the normal state should arise
from such defects in the conducting FeSe layers. $A_x$Fe$_2$Se$_2$ ($A$ = K,
Rb, and Cs) single crystals show the same susceptibility behavior in the normal
state, and no anomaly is observed in susceptibility at the hump temperature in
resistivity. The clear jump in specific heat for Rb$_x$Fe$_2$Se$_2$ and
K$_x$Fe$_2$Se$_2$ single crystals shows the good bulk superconductivity in
these crystals. | 1101.5670v1 |
2011-03-04 | Measurements of thermodynamic and transport properties of EuC$_2$: a low-temperature analogue of EuO | EuC$_2$ is a ferromagnet with a Curie-temperature of $T_C \simeq 15\,$K. It
is semiconducting with the particularity that the resistivity drops by about 5
orders of magnitude on cooling through $T_C$, which is therefore called a
metal-insulator transition. In this paper we study the magnetization, specific
heat, thermal expansion, and the resistivity around this ferromagnetic
transition on high-quality EuC$_2$ samples. At $T_C$ we observe well defined
anomalies in the specific heat $c_p(T)$ and thermal expansion $\alpha(T)$ data.
The magnetic contributions of $c_p(T)$ and $\alpha(T)$ can satisfactorily be
described within a mean-field theory, taking into account the magnetization
data. In zero magnetic field the magnetic contributions of the specific heat
and thermal expansion fulfill a Gr\"uneisen-scaling, which is not preserved in
finite fields. From an estimation of the pressure dependence of $T_C$ via
Ehrenfest's relation, we expect a considerable increase of $T_C$ under applied
pressure due to a strong spin-lattice coupling. Furthermore the influence of
weak off stoichiometries $\delta$ in EuC$_{2 \pm \delta}$ was studied. It is
found that $\delta$ strongly affects the resistivity, but hardly changes the
transition temperature. In all these aspects, the behavior of EuC$_2$ strongly
resembles that of EuO. | 1103.0980v1 |
2012-07-13 | Synthesis and acid resistance of maya blue pigment | Maya blue is an organo-clay artificial pigment composed of indigo and
palygorskite. It was invented and frequently used in Mesoamerica in ancient
times (eighth to 16th centuries). We analyse in this paper one of the
characteristics of Maya blue that has attracted the attention of scientists
since its rediscovery in 1931: its high stability against chemical aggression
(acids, alkalis, solvents, etc.) and biodegradation, which has permitted the
survival of many works of art for centuries in hostile environments, such as
the tropical forest. We have reproduced the different methods proposed to
produce a synthetic pigment with the characteristics of the ancient Maya blue.
The stability of the pigments produced using either palygorskite or sepiolite
has been analysed by performing acid attacks of different intensities. The
results are analysed in terms of pigment decolouration and destruction of the
clay lattice, revealed by X-ray diffraction. Palygorskite pigments are much
more resistant than sepiolite pigments. It is shown that indigo does not
protect the clay lattice against acid aggression. We show that Maya blue is an
extremely resistant pigment, but it can be destroyed using very intense acid
treatment under reflux. | 1207.3229v1 |
2013-04-07 | Quasi-classical physics and T-linear resistivity in both strongly correlated and ordinary metals | We show that near a quantum critical point generating quantum criticality of
strongly correlated metals where the density of electron states diverges, the
quasi-classical physics remains applicable to the description of the
resistivity \rho of strongly correlated metals due to the presence of a
transverse zero-sound collective mode, reminiscent of the phonon mode in
solids. We demonstrate that at T, being in excess of an extremely low Debye
temperature T_D, the resistivity \rho(T) changes linearly with T, since the
mechanism, forming the T dependence of \rho(T), is the same as the
electron-phonon mechanism that prevails at high temperatures in ordinary
metals. Thus, electron-phonon scattering leads to near material-independence of
the lifetime \tau of quasiparticles that is expressed as the ratio of the
Planck constant \hbar to the Boltzmann constant k_B, T\tau\sim \hbar/k_B. We
find that at T<T_D there exists a different mechanism, maintaining the T-linear
dependence of \rho(T), and making the constancy of \tau fail in spite of the
presence of T-linear dependence. Our results are in good agreement with
exciting experimental observations. | 1304.2068v4 |
2013-09-13 | 1/f noise in graphene | We present a novel and comprehensive model of 1/f noise in nanoscale graphene
devices that accounts for the unusual and so far unexplained experimental
characteristics. We find that the noise power spectral density versus carrier
concentration of single-layer sheet devices has a behavior characterized by a
shape going from the M to the Gamma type as the material inhomogeneity
increases, whereas the shape becomes of V type in bilayer sheet devices for any
inhomogeneity, or of M type at high carrier concentration. In single-layer
nanoribbons, instead, the ratio of noise to resistance versus the latter
quantity is approximately constant, whereas in the bilayer case it exhibits a
linear decrease on a logarithmic scale as resistance increases and its limit
for zero resistance equals the single-layer value. Noise at the Dirac point is
much greater in single-layer than in bilayer devices and it increases with
temperature. The origin of 1/f noise is attributed to the traps in the device
and to their relaxation time dispersion. The coupling of trap charge
fluctuations with the electrode current is computed according to the
electrokinematics theorem, by taking into account their opposite effects on
electrons and holes as well as the device inhomogeneities. The results agree
well with experiments. | 1309.3420v1 |
2014-09-19 | Absence of a quantum limit to charge diffusion in bad metals | Good metals are characterised by diffusive transport of coherent
quasi-particle states and the resistivity is much less than the
Mott-Ioffe-Regel (MIR) limit, $\frac{ha}{e^{2}}$, where $a$ is the lattice
constant. In bad metals, such as many strongly correlated electron materials,
the resistivity exceeds the Mott-Ioffe-Regel limit and the transport is
incoherent in nature. Hartnoll, loosely motivated by holographic duality
(AdS/CFT correspondence) in string theory, recently proposed a lower bound to
the charge diffusion constant, $D \gtrsim \hbar v_{F}^{2}/(k_{B}T)$, in the
incoherent regime of transport, where $v_F$ is the Fermi velocity and $T$ the
temperature. Using dynamical mean field theory (DMFT) we calculate the charge
diffusion constant in a single band Hubbard model at half filling. We show that
in the strongly correlated regime the Hartnoll's bound is violated in the
crossover region between the coherent Fermi liquid region and the incoherent
(bad metal) local moment region. The violation occurs even when the bare Fermi
velocity $v_F$ is replaced by its low temperature renormalised value,
$v_F^*$.The bound is satisfied at all temperatures in the weakly and moderately
correlated systems as well as in strongly correlated systems in the high
temperature region where the resistivity is close to linear in temperature. Our
calculated charge diffusion constant, in the incoherent regime of transport,
also strongly violates a proposed quantum limit of spin diffusion, $D_{s} \sim
1.3 \hbar/m$, where $m$ is the fermion mass, experimentally observed and
theoretically calculated in a cold degenerate Fermi gas in the unitary limit of
scattering. | 1409.5662v2 |
2016-05-26 | Fast suppression of superconductivity with Fe site Ni substitution in Fe1-xNixSe0.5Te0.5 (x=0.0, 0.01, 0.03, 0.05, 0.07, 0.10 and 0.20) single crystals | We report the effect of Ni doping on superconductivity of FeSe0.5Te0.5. The
single crystal samples of series Fe1-xNixSe0.5Te0.5 (x=0.0, 0.01, 0.03, 0.05,
0.07, 0.10 and 0.20) are synthesized via vacuum shield solid state reaction
route and high temperature heating followed by slow cooling. All the crystals
of Fe1-xNixSe0.5Te0.5 series with x up to 0.20, i.e., 20% substitution of Ni at
Fe site are crystallized in single phase tetragonal structure with space group
P4/nmm. The electrical resistivity measurements revealed that Tc decreases fast
with increase of Ni concentration in Fe1-xNixSe0.5Te0.5. Namely the
superconducting transition temperature (Tc) being defined as resistivity =0
decrease from 12K to around 4K and 2K for x=0.01 and 0.03 samples respectively.
For x=0.05 (5at% Ni at Fe site) though Tconset is observed in resistivity
measurements but \r{ho}=0 is not seen down to 2K. For x more than 0.07, neither
the Tconset nor Tc\r{ho}=0 is seen down 2K in R-T measurements. It is
demonstrated that Ni doping at Fe site in FeSe0.5Te0.5 superconductor
suppresses superconductivity fast. The rate of Tc depression is albeit non
monotonic. Summarily, a systematic study on suppression of superconductivity
with Fe site Ni doping in flux free gown FeSe0.5Te0.5 single crystals is
presented in the current communication. | 1605.08217v2 |
2016-06-23 | Resistive properties and phase diagram of the organic antiferromagnetic metal $κ$-(BETS)$_2$FeCl$_4$ | The low-temperature electronic state of the layered organic charge-transfer
salt $\kappa$-(BETS)$_2$FeCl$_4$ was probed by interlayer electrical resistance
measurements under magnetic field. Both above and below
$T_{\mathrm{N}}=0.47\,$K, the temperature of antiferromagnetic ordering of
$3d$-electron spins of Fe$^{3+}$ localized in the insulating anion layers, a
non-saturating linear $R(T)$ dependence has been observed. A weak
superconducting signal has been detected in the antiferromagnetic state, at
temperatures $\leq 0.2\,$K. Despite the very high crystal quality, only a tiny
fraction of the sample appears to be superconducting. Besides a small kink
feature in the resistivity, the impact of the antiferromagnetic ordering of
localized Fe$^{3+}$ spins on the conduction $\pi$-electron system is clearly
manifested in the Fermi surface reconstruction, as evidenced by Shubnikov-de
Haas oscillations. The "magnetic field -- temperature" phase diagrams for the
field directions parallel to each of the three principal crystal axes have been
determined. For magnetic field along the easy axis a spin-flop transition has
been found. Similarities and differences between the present material and the
sister compound $\kappa$-(BETS)$_2$FeBr$_4$ are discussed. | 1606.07331v3 |
2016-10-28 | Asymmetric pentagonal metal meshes for flexible transparent electrodes and heaters | Metal meshes have emerged as an important class of flexible transparent
electrodes. We report on the characteristics of a new class of asymmetric
meshes, tiled using a recently-discovered family of pentagons. Micron-scale
meshes were fabricated on flexible polyethylene terephthalate substrates via
optical lithography, metal evaporation (Ti 10 nm, Pt 50 nm) and lift-off. Three
different designs were assessed, each with the same tessellation pattern and
linewidth (5 micron), but with different sizes of the fundamental pentagonal
unit. The designs corresponded to areal coverage of the metal patterns of 27%
(Design#1), 14% (Design#2) and 9% (Design#3), respectively. Good mechanical
stability was observed for both tensile strain and compressive strain. After
1,000 bending cycles, devices subjected to tensile strain showed fractional
resistance increases in the range 8% to 17% with the lowest changes observed
for Design#2. Devices subjected to compressive strain showed fractional
resistance increases in the range 0% to 7% with best results observed for
Design#1. The performance of the pentagonal metal mesh devices as visible
transparent heaters via Joule heating was also assessed. A saturation
temperature of 88 +/- 1 degrees C was achieved at low voltage (5 V) with a fast
response time (~ 20 s) and a high thermal resistance (168 +/- 6 degrees C
cm2/W). Finally, de-icing was successfully demonstrated (45 s at 5 V) for an
ice layer on a glass coupon placed on top of the PET substrate. | 1611.02744v1 |
2018-11-06 | Metallic surface states in a correlated d-electron topological Kondo insulator candidate FeSb2 | The resistance of a conventional insulator diverges as temperature approaches
zero. The peculiar low temperature resistivity saturation in the 4f Kondo
insulator (KI) SmB6 has spurred proposals of a correlation-driven topological
Kondo insulator (TKI) with exotic ground states. However, the scarcity of model
TKI material families leaves difficulties in disentangling key ingredients from
irrelevant details. Here we use angle-resolved photoemission spectroscopy
(ARPES) to study FeSb2, a correlated d-electron KI candidate that also exhibits
a low temperature resistivity saturation. On the (010) surface, we find a rich
assemblage of metallic states with two-dimensional dispersion. Measurements of
the bulk band structure reveal band renormalization, a large
temperature-dependent band shift, and flat spectral features along certain high
symmetry directions, providing spectroscopic evidence for strong correlations.
Our observations suggest that exotic insulating states resembling those in SmB6
and YbB12 may also exist in systems with d instead of f electrons. | 1811.02183v3 |
2016-03-09 | Quantization of Hall Resistance at the Metallic Interface between an Oxide Insulator and SrTiO$_{3}$ | The two-dimensional metal forming at the interface between an oxide insulator
and SrTiO3 provides new opportunities for oxide electronics. However, the
quantum Hall effect, one of the most fascinating effects of electrons confined
in two dimensions, remains underexplored at these complex oxide
heterointerfaces. Here, we report the experimental observation of quantized
Hall resistance in a SrTiO3 heterointerface based on the modulation-doped
amorphous-LaAlO$_{3}$/SrTiO$_{3}$ heterostructure, which exhibits both high
electron mobility exceeding 10000 cm$^{2}$/Vs and low carrier density on the
order of ~10$^{12}$ cm$^{-2}$. Along with unambiguous Shubnikov-de Haas
oscillations, the spacing of the quantized Hall resistance suggests that the
interface is comprised of a single quantum well with ten parallel conducting
two-dimensional subbands. This provides new insight into the electronic
structure of conducting oxide interfaces and represents an important step
towards designing and understanding advanced oxide devices. | 1603.02850v2 |
2017-07-21 | Electrical characterization of structured platinum diselenide devices | Platinum diselenide (PtSe2) is an exciting new member of the two-dimensional
(2D) transition metal dichalcogenide (TMD) family. it has a semimetal to
semiconductor transition when approaching monolayer thickness and has already
shown significant potential for use in device applications. Notably, PtSe2 can
be grown at low temperature making it potentially suitable for industrial
usage. Here, we address thickness dependent transport properties and
investigate electrical contacts to PtSe2, a crucial and universal element of
TMD-based electronic devices. PtSe2 films have been synthesized at various
thicknesses and structured to allow contact engineering and the accurate
extraction of electrical properties. Contact resistivity and sheet resistance
extracted from transmission line method (TLM) measurements are compared for
different contact metals and different PtSe2 film thicknesses. Furthermore, the
transition from semimetal to semiconductor in PtSe2 has been indirectly
verified by electrical characterization of field-effect devices. Finally, the
influence of edge contacts at the metal - PtSe2 interface has been studied by
nanostructuring the contact area using electron beam lithography. By increasing
the edge contact length, the contact resistivity was improved by up to 70%
compared to devices with conventional top contacts. The results presented here
represent crucial steps towards realizing high-performance nanoelectronic
devices based on group-10 TMDs. | 1707.06824v1 |
2017-08-06 | Electric-field-induced extremely large change in resistance in graphene ferromagnets | A colossal magnetoresistance ($\sim 100\times10^3\%$) and an extremely large
magnetoresistance ($\sim 1\times10^6\%$) have been previously explored in
manganite perovskites and Dirac materials, respectively. However, the
requirement of an extremely strong magnetic field (and an extremely low
temperature) makes them not applicable for realistic devices. In this work, we
propose a device that can generate even larger changes in resistance in a
zero-magnetic field and at a high temperature. The device is composed of a
graphene under two strips of yttrium iron garnet (YIG), where two gate voltages
are applied to cancel the heavy charge doping in the YIG-induced half-metallic
ferromagnets. By calculations using the Landauer-B\"{u}ttiker formalism, we
demonstrate that, when a proper gate voltage is applied on the free
ferromagnet, changes in resistance up to $305\times10^6\%$ ($16\times10^3\%$)
can be achieved at the liquid helium (nitrogen) temperature and in a zero
magnetic field. We attribute such a remarkable effect to a gate-induced
full-polarization reversal in the free ferromagnet, which results in a
metal-state to insulator-state transition in the device. We also find that, the
proposed effect can be realized in devices using other magnetic insulators such
as EuO and EuS. Our work should be helpful for developing a realistic switching
device that is energy saving and CMOS-technology compatible. | 1708.01858v2 |
2018-08-30 | Metallic glasses for spintronics: anomalous temperature dependence and giant enhancement of inverse spin Hall effect | Spin-charge conversion via inverse spin Hall effect (ISHE) is essential for
enabling various applications of spintronics. The spin Hall response usually
follows a universal scaling relation with longitudinal electric resistivity and
has mild temperature dependence because elementary excitations play only a
minor role in resistivity and hence ISHE. Here we report that the ISHE of
metallic glasses shows nearly two orders of magnitude enhancements with
temperature increase from a threshold of 80-100 K to glass transition points.
As electric resistivity changes only marginally in the temperature range, the
anomalous temperature dependence is in defiance of the prevailing scaling law.
Such a giant temperature enhancement can be well described by a two-level
thermal excitation model of glasses and disappears after crystallization,
suggesting a new mechanism which involves unique thermal excitations of
glasses. This finding may pave new ways to achieve high spin-charge conversion
efficiency at room and higher temperatures for spintronic devices and to detect
structure and dynamics of glasses using spin currents. | 1808.10371v1 |
2018-07-06 | MRPC3b mass production for CBM-TOF and eTOF at STAR | The Compressed Baryonic Matter (CBM) spectrometer aims to study strongly
interacting matter under extreme conditions. The key element providing hadron
identification at incident energies between 2 and 11 AGeV in heavy-ion
collisions at the SIS100 accelerator is a Time-of-Flight (TOF) wall covering
the polar angular range from $2.5^0$ --$25^0$ and full azimuth. CBM is expected
to be operational in the year 2024 at the Facility for Anti-proton and Ion
Research (FAIR) in Darmstadt, Germany. The existing conceptual design foresees
a 120 m^2 TOF-wall composed of Multi-gap Resistive Plate Chambers (MRPC) which
is subdivided into a high rate region, a middle rate region and a low rate
region. The MRPC3b Multistrip-MRPCs, foreseen to be integrated in the low rate
region, have to cope with charged particle fluxes up to 1 kHz/cm2 and therefore
will be constructed with thin float glass (0.28 mm thickness) as resistive
electrode material. In the scope of the FAIR phase 0 program it is planned to
install about 36 \% of the MRPC3b counters in the east endcap region of the
STAR experiment at BNL as an upgrade for the Beam Energy Scan campaign (BESII)
in 2019/2020. | 1807.02452v1 |
2019-01-03 | Study of electrostatic septum design and its high-voltage discharge protection | In this paper, we introduce the design of electrostatic septum (ESS) for the
accelerator of Shanghai Advanced Proton Therapy (SAPT), and discuss its
mechanical structure and the material selection of the electrode. The beam loss
on the septum is studied, and the calculation results are given by the particle
simulation and by the formula which is related to the placement angle and the
divergence angle in the horizontal direction. Considering the thermal effect of
the beam loss on the head of the septum, the equilibrium temperature at work is
calculated. In addition, the distribution of the electric field and the
trajectory of the particles are also simulated. The phenomenon of vacuum
discharge in the working ESS is analyzed in detail on the relationship between
the working current and the enhancement factor of the electric field on the
electrode surface. Based on the discharge mechanism, the importance of
degassing and cleaning of ESS is analyzed. We also analyzed the effect of
external series resistance from circuit and discharge mechanism. It is
considered that series resistance within a certain range can increase the
breakdown voltage between vacuum electrodes and reduce the irreversible damage
to the surface of the electrode system caused by the discharge process. The
formula for the value of the resistance is given. | 1901.00646v3 |
2020-05-17 | Remarkable low-energy properties of the pseudogapped semimetal Be$_5$Pt | We report measurements and calculations on the properties of the
intermetallic compound Be$_5$Pt. High-quality polycrystalline samples show a
nearly constant temperature dependence of the electrical resistivity over a
wide temperature range. On the other hand, relativistic electronic structure
calculations indicate the existence of a narrow pseudogap in the density of
states arising from accidental approximate Dirac cones extremely close to the
Fermi level. A small true gap of order 3 meV is present at the Fermi level, yet
the measured resistivity is nearly constant from low to room temperature. We
argue that this unexpected behavior can be understood by a cancellation of the
energy dependence of density of states and relaxation time due to disorder, and
discuss a model for electronic transport. With applied pressure, the
resistivity becomes semiconducting, consistent with theoretical calculations
that show that the band gap increases with applied pressure. We further discuss
the role of Be inclusions in the samples. | 2005.08327v2 |
2021-04-19 | Various magnetism of the compressed antiferromagnetic topological insulator EuSn2As2 | We report a comprehensive high-pressure study on the antiferromagnetic
topological insulator EuSn2As2 up to 21.1 GPa through measurements of
synchrotron x-ray diffraction, electrical resistance, magnetic resistance, and
Hall transports combined with first-principles calculations. No evident trace
of a structural phase transition is detected. The Neel temperatures determined
from resistance are increased from 24 to 77 K under pressure, which is resulted
from the enhanced magnetic exchange couplings between Eu2+ ions yielded by our
first-principles calculations. The negative magnetoresistance of EuSn2As2
persists to higher temperatures accordantly. However, the enhancement of the
observed N\'eel temperatures deviates from the calculations obviously above
10.0 GPa. In addition, the magnitude of the magnetoresistance, the Hall
coefficients, and the charge carrier densities show abrupt changes between 6.9
to 10.0 GPa. The abrupt changes probably originate from a pressure induced
valence change of Eu ions from a divalent state to a divalent and trivalent
mixed state. Our results provide insights into variation of the magnetism of
EuSn2As2 and similar antiferromagnetic topological insulators under pressure. | 2104.09412v1 |
2021-04-20 | Properties of MoO2 and MoO3 Films Prepared from the Chemically Driven Isothermal Close Space Vapor Transport Technique | Chemically _ driven isothermal close space vapour transport was used to
prepare pure MoO2 films which were eventually converted to MoO3 by annealing in
air. According to temperature_dependent Raman measurements, the MoO2/MoO3 phase
transformation was found to occur in the 225 _ 350 oC range; no other phases
were detected during the transition. A clear change in composition and Raman
spectra, as well as noticeable modifications of the band gap and the absorption
coefficient confirmed the conversion from MoO2 to MoO3. An extensive
characterization of films of both pure phases was carried out. In particular, a
procedure was developed to determine the dispersion relation of the refractive
index of MoO2 from the shift of the interference fringes the used SiO2/Si
substrate. The obtained refractive index was corrected taking into account the
porosity calculated from elastic backscattering spectrometry. The Debye
temperature and the residual resistivity were extracted from the electrical
resistivity temperature dependence using the Bloch _ Gruneisen equation. MoO3
converted samples presented very high resistivity and a typical semiconducting
behaviour. They also showed intense and broad luminescence spectra, which were
deconvoluted considering several contributions; and its behaviour with
temperature was examined. Furthermore, surface photovoltage spectra were taken
and the relation of these spectra with the photoluminescence is discussed. | 2104.10245v1 |
2021-08-21 | Evolution of superconductivity and charge order in pressurized RbV$_3$Sb$_5$ | The kagome metals $A$V$_3$Sb$_5$ ($A=$ K, Rb, Cs) under ambient pressure
exhibit an unusual charge order, from which superconductivity emerges. In this
work, by applying hydrostatic pressure using a liquid pressure medium and
carrying out electrical resistance measurements for RbV$_3$Sb$_5$, we find the
charge order becomes suppressed under a modest pressure $p_{\rm c}$
($1.4<p_{\rm c}<1.6$ GPa), while the superconducting transition temperature
$T_{\rm c}$ is maximized. $T_{\rm c}$ is then gradually weakened with further
increase of pressure and reaches a minimum around 14.3 GPa, before exhibiting
another maximum around 22.8 GPa, signifying the presence of a second
superconducting dome. Distinct normal state resistance anomalies are found to
be associated with the second superconducting dome, similar to KV$_3$Sb$_5$.
Our findings point to qualitatively similar temperature-pressure phase diagrams
in KV$_3$Sb$_5$ and RbV$_3$Sb$_5$, and suggest a close link between the second
superconducting dome and the high-pressure resistance anomalies. | 2108.09434v2 |
2021-08-22 | Explainable Machine Learning using Real, Synthetic and Augmented Fire Tests to Predict Fire Resistance and Spalling of RC Columns | This paper presents the development of systematic machine learning (ML)
approach to enable explainable and rapid assessment of fire resistance and
fire-induced spalling of reinforced concrete (RC) columns. The developed
approach comprises of an ensemble of three novel ML algorithms namely; random
forest (RF), extreme gradient boosted trees (ExGBT), and deep learning (DL).
These algorithms are trained to account for a wide collection of geometric
characteristics and material properties, as well as loading conditions to
examine fire performance of normal and high strength RC columns by analyzing a
comprehensive database of fire tests comprising of over 494 observations. The
developed ensemble is also capable of presenting quantifiable insights to ML
predictions; thus, breaking free from the notion of 'blackbox' ML and
establishing a solid step towards transparent and explainable ML. Most
importantly, this work tackles the scarcity of available fire tests by
proposing new techniques to leverage the use of real, synthetic and augmented
fire test observations. The developed ML ensemble has been calibrated and
validated for standard and design fire exposures and for one, two, three and
four-sided fire exposures thus; covering a wide range of practical scenarios
present during fire incidents. When fully deployed, the developed ensemble can
analyze over 5,000 RC columns in under 60 seconds thus, providing an attractive
solution for researchers and practitioners. The presented approach can also be
easily extended for evaluating fire resistance and spalling of other structural
members and under varying fire scenarios and loading conditions and hence paves
the way to modernize the state of this research area and practice. | 2108.09862v1 |
2021-11-27 | Antiferromagnetism and large magnetoresistance in GdBi single crystal | Single crystal of the binary equi-atomic compound GdBi crystallizing in the
rock salt type cubic crystal structure with the space group $Fm\bar{3}m$ has
been grown by flux method. The electrical and magnetic measurements have been
performed on well oriented single crystals. The antiferromagnetic ordering of
the Gd moments is confirmed at $T_{\rm N} = 27.5$~K. The magnetization
measurement performed at $2$~K along the principal crystallographic direction
[100] did not show any metamagnetic transition and no sign of saturation up to
$7$~T. Zero field electrical resistivity reveals a sharp drop at $27.5$~K
suggesting a reduction in the spin disorder scattering due to the
antiferromagnetic alignment of the Gd moments. The residual resistivity at
$2$~K is 390~n$\Omega$cm suggesting a good quality of the grown crystal. The
magneto resistance attains a value of $1.0~\times~10^{4}\%$ with no sign of
saturation, in a field of $14$~T, at $T = 2$~K. Shubnikov de Hass (SdH)
oscillations have been observed in the high field range of the
magnetoresistance with five different frequencies corresponding to the extremal
areas of the Fermi surface. Analysis of the Hall data revealed a near
compensation of the charge carriers accounting for the extremely large
magnetoresistance. | 2111.13836v1 |
2022-06-13 | Ultra-High-Precision Detection of Single Microwave Photons based on a Hybrid System between Majorana Zero Mode and a Quantum Dot | The ability to detect single photons has become increasingly essential due to
the rise of photon-based quantum computing. In this theoretical work, we
propose a system consisting of a quantum dot (QD) side-coupled to a
superconducting nanowire. The coupling opens a gap in both the QD mode and the
Majorana zero mode (MZM) at the nanowire edge, enabling photon absorption in
the system. We show that the absorbed photoelectron decays via rapid
(sub-nanosecond to nanosecond) nonradiative heat transfer to the nanowire
phonon modes rather than by spontaneous emission. Furthermore, we calculate the
temperature increase and associated resistance increase induced by the
absorption of a photon for a given appropriate set of material and
environmental parameters, yielding a temperature increase in the millikelvin
range and a resistance increase in the kiloohm range, vastly exceeding the
photon-absorption-induced temperature and resistance increases for competing
2D-3D hybrid systems by 5 and 9 orders of magnitude, respectively. Lastly, we
determine the detector efficiency and discuss the system density required for
deterministic photon number measurement, demonstrating that a photon absorption
probability of over 99.9 percent can be achieved for an integrated system
consisting of an array of nanowire-QD complexes on-chip inside a cavity. Our
results thus provide a basis for a deterministic microwave photon number
detector with an unprecedented photon-number-detection resolution. | 2206.06521v4 |
2022-11-02 | Beta-Ga2O3 MOSFETs with near 50 GHz fMAX and 5.4 MV/cm average breakdown field | This letter reports high-performance $\mathrm{\beta} Ga2O3 thin channel
MOSFETs with T-gate and degenerately doped source/drain contacts regrown by
MOCVD. Gate length scaling (LG= 160-200 nm) leads to a peak drain current
(ID,MAX) of 285 mA/mm and peak trans-conductance (gm) of 52 mS/mm at 10 V drain
bias with 23.5 Ohm mm on resistance (Ron). A low metal/n+ contact resistance of
0.078 Ohm mm was extracted from TLM measurement. Ron is dominated by interface
resistance between channel and regrown layer. A gate-to-drain breakdown voltage
of 192 V is measured for LGD = 355 nm resulting in average breakdown field
(E_AVG) of 5.4 MV/cm. This E_AVG is the highest reported among all sub-micron
gate length lateral FETs. RF measurements on 200 nm Silicon Nitride (Si3N4)
passivated device shows a current gain cut off frequency (f_T) of 11 GHz and
record power gain cut off frequency (f_MAX) of 48 GHz. The f_T.V_Br product is
2.11 THz.V for 192 V breakdown voltage. The switching figure of merit exceeds
that of silicon and is comparable to mature wide-band gap devices. | 2211.01088v1 |
2023-04-06 | All-electrical operation of a Curie-switch at room temperature | We present all-electrical operation of a Fe$_x$Cr$_{1-x}$-based Curie switch
at room temperature. More specifically, we study the current-induced
thermally-driven transition from ferromagnetic to antiferromagnetic
Ruderman-Kittel-Kasuya-Yosida (RKKY) indirect coupling in a
Fe/Cr/Fe$_{17.5}$Cr$_{82.5}$/Cr/Fe multilayer. Magnetometry measurements at
different temperatures show that the transition from the ferromagnetic to the
antiferromagnetic coupling at zero field is observed at $\sim$325K. Analytical
modelling confirms that the observed temperature-dependent transition from
indirect ferromagnetic to indirect antiferromangetic interlayer exchange
coupling originates from the modification of the effective interlayer exchange
constant through the ferromagnetic-to-paramagnetic transition in the
Fe$_{17.5}$Cr$_{82.5}$ spacer with minor contributions from the
thermally-driven variations of the magnetization and magnetic anisotropy of the
Fe layers. Room-temperature current-in-plane magnetotransport measurements on
the patterned Fe/Cr/Fe$_{17.5}$Cr$_{82.5}$/Cr/Fe strips show the transition
from the 'low-resistance' parallel to the 'high-resistance' antiparallel
remanent magnetization configuration, upon increased probing current density.
Quantitative comparison of the switching fields, obtained by magnetometry and
magnetotransport, confirms that the Joule heating is the main mechanism
responsible for the observed current-induced resistive switching. | 2304.03040v2 |
2023-05-14 | Response of the Verwey transition in magnetite to a controlled point-like disorder induced by 2.5 MeV electron irradiation | A controlled point-like disorder induced by low temperature 2.5 MeV electron
irradiation was used to probe the nature of the Verwey transition in magnetite,
$\text{Fe}_{3}\text{O}_{4}$. Two large single crystals, one with optimal
transition temperature, $T_{V}\approx121$ K, and another with $T_{V}\approx109$
K, as well as biogenic nanocrystals, $T_{V}\approx110$ K, were examined.
Temperature-dependent resistivity is consistent with the
semiconductor-to-semiconductor sharp, step-like Verwey transition from a state
with a small bandgap of around 60 meV to a state with a larger bandgap of about
300 meV. The irradiation causes an up-shift of the resistivity curves above the
transition without transition smearing or broadening. It also causes an
apparent down-shift of the resistivity maximum at high temperatures. In the
lower $T_{V}$ crystal, the electron irradiation drives the transition
temperature into a ``forbidden" regime believed to separate the first order
from the second order phase transition. Contrary to this belief, the transition
itself remains sharp and hysteretic without a significant change in the
hysteresis width. We conclude that the sudden change of the bandgap accompanied
by the monoclinic distortion and the change of magnetic anisotropy is the
reason for the Verwey transition in magnetite and the effect of additional
disorder is mostly in the smearing of the sharp gap edges near the Fermi level. | 2305.08276v1 |
2023-09-12 | Numerical study on the effects of fluid properties in electrohydrodynamic pulsating jet under constant voltage | Pulsating jet is one of the common working modes in electrohydrodynamic
printing (EHDP) that process is highly affected by operating parameters and
material properties. In this paper, the processes of pulsating jet for liquids
with different physical properties were investigated using numerical
simulation. An electrohydrodynamic solver was established, and a charge flux
restricting step was adopted to ensure a realistic distribution of free
charges. Three various ejection regimes were observed in our simulations:
oscillating cone (OC), choked jet (CJ), and stable cone-jet (SJ). We found that
three dimensionless numbers relating to liquid properties determined the
ejection regime: the Ohnesorge number, Q0{\epsilon}r/Q, and Q0/(QRe). Based on
those dimensionless numbers, the roles of liquid properties on pulsating jet
(OC and CJ) were analyzed. In OC, the break of the jet is due to the
significant oscillation of the Taylor cone, which is mainly affected by
viscosity and conductivity. In CJ, the jet emission is terminated by the
excessive resistant force in the cone-jet transition region. For liquids with
low and medium viscosity, the dominant resistant force is the polarization
force or viscous force when {\epsilon}rRe is larger or smaller than 1,
respectively. For high viscosity liquids, the viscous force always becomes the
major resistance. These results further reveal the physical mechanism of
pulsating jet and can be used to guide its application. | 2309.06277v1 |
2023-10-13 | Controlling Umklapp scattering in bilayer graphene moir'e superlattice | In this Letter, we present experimental findings on electron-electron
scattering in a two-dimensional moir'e heterostructure with tunable Fermi wave
vector, reciprocal lattice vector, and band gap. We achieve this in
high-mobility aligned heterostructures of bilayer graphene (BLG) and hBN.
Around half-filling, the primary contribution to the resistance of BLG/hBN
aligned superlattices arises from electron-electron Umklapp (Uee) scattering,
making the resistance of graphene/hBN moir'e devices significantly larger than
that of non-aligned devices (where Uee is forbidden). We quantify the strength
of the Uee scattering and find that it follows a universal scaling with Fermi
energy and has a non-monotonic dependence on the charge carrier density. The
Uee scattering is strongly electric field tunable and affected by
layer-polarization of BLG. It has a strong particle-hole asymmetry - the
resistance when the chemical potential is in the conduction band is
significantly lesser than when it is in the valence band, making the
electron-doped regime more practical for potential applications. | 2310.08906v2 |
2023-11-20 | Absence of metallicity and bias-dependent resistivity in low-carrier-density EuCd2As2 | EuCd2As2 was theoretically predicted to be a minimal model of Weyl semimetals
with a single pair of Weyl points in the ferromagnet state. However, the
heavily p-doped EuCd2As2 crystals in previous experiments prevent direct
identification of the semimetal hypothesis. Here we present a comprehensive
magneto-transport study of high-quality EuCd2As2 crystals with ultralow bulk
carrier density (10^13 cm-3). In contrast to the general expectation of a Weyl
semimetal phase, EuCd2As2 shows insulating behavior in both antiferromagnetic
and ferromagnetic states as well as surface-dominated conduction from band
bending. Moreover, the application of a dc bias current can dramatically
modulate the resistance by over one order of magnitude, and induce a periodic
resistance oscillation due to the geometric resonance. Such nonlinear transport
results from the highly nonequilibrium state induced by electrical field near
the band edge. Our results suggest an insulating phase in EuCd2As2 and put a
strong constraint on the underlying mechanism of anomalous transport properties
in this system. | 2311.11515v1 |
2024-01-15 | Alternating Bias Assisted Annealing of Amorphous Oxide Tunnel Junctions | We demonstrate a transformational technique for controllably tuning the
electrical properties of fabricated thermally oxidized amorphous aluminum-oxide
tunnel junctions. Using conventional test equipment to apply an alternating
bias to a heated tunnel barrier, giant increases in the room temperature
resistance, greater than 70%, can be achieved. The rate of resistance change is
shown to be strongly temperature-dependent, and is independent of junction size
in the sub-micron regime. In order to measure their tunneling properties at mK
temperatures, we characterized transmon qubit junctions treated with this
alternating-bias assisted annealing (ABAA) technique. The measured frequencies
follow the Ambegaokar-Baratoff relation between the shifted resistance and
critical current. Further, these studies show a reduction of
junction-contributed loss on the order of $\approx 2 \times10^{-6}$, along with
a significant reduction in resonant- and off-resonant-two level system defects
when compared to untreated samples. Imaging with high-resolution TEM shows that
the barrier is still predominantly amorphous with a more uniform distribution
of aluminum coordination across the barrier relative to untreated junctions.
This new approach is expected to be widely applicable to a broad range of
devices that rely on amorphous aluminum oxide, as well as the many other
metal-insulator-metal structures used in modern electronics. | 2401.07415v2 |
2024-01-22 | Self-pulsing of Dielectric Barrier Discharges at Low Driving Frequencies | This paper investigates the self-pulsing of Dielectric Barrier Discharges
(DBDs) at low driving frequencies. In particular, (a) the dependence of current
on the product pd of gas pressure p and the gas gap length d, (b) the effects
of lossy dielectrics (in resistive discharges) and large dielectric
permittivity (in ferroelectrics) on current dynamics, (c) the transition from
Townsend to a dynamic Capacitively Coupled Plasma (CCP) discharge with changing
pd values, and (d) the transition from Townsend to a high-frequency CCP regime
with increasing the driving frequency. A one-dimensional fluid model of Argon
plasma is coupled to an equivalent RC circuit for lossy dielectrics. Our
results show multiple current pulses per AC period in Townsend and CCP
discharge modes which are explained by uncoupled electron-ion transport in the
absence of quasineutrality and surface charge deposition at dielectric
interfaces. The number of current pulses decreases with an increasing applied
frequency when the Townsend discharge transforms into the CCP discharge. The
resistive barrier discharge with lossy dielectrics exhibits Townsend and glow
modes for the same pd value (7.6 Torr cm) for higher and lower resistances,
respectively. Finally,we show that ferroelectric materials can amplify
discharge current in DBDs. Similarities between current pulsing in DBD, Trichel
pulses in corona discharges, and subnormal oscillations in DC discharges are
discussed. 1 | 2401.12410v3 |
2015-06-26 | Conventional superconductivity at 203 K at high pressures | A superconductor is a material that can conduct electricity with no
resistance below its critical temperature (Tc). The highest Tc that has been
achieved in cuprates1 is 133 K at ambient pressure2 and 164 K at high
pressures3. As the nature of superconductivity in these materials has still not
been explained, the prospects for a higher Tc are not clear. In contrast, the
Bardeen-Cooper-Schrieffer (BCS) theory gives a guide for achieving high Tc and
does not put bounds on Tc, all that is needed is a favorable combination of
high frequency phonons, strong electron-phonon coupling, and a high density of
states. These conditions can be fulfilled for metallic hydrogen and covalent
compounds dominated by hydrogen4,5. Numerous calculations support this idea and
predict Tc of 50-235 K for many hydrides6 but only moderate Tc=17 K has been
observed experimentally7. Here we studied sulfur hydride8 where a Tc~80 K was
predicted9. We found that it transforms to a metal at pressure ~90 GPa. With
cooling superconductivity was found deduced from a sharp drop of the
resistivity to zero and a decrease of Tc with magnetic field. The pronounce
isotope shift of Tc in D2S is evidence of an electron-phonon mechanism of
superconductivity that is consistent with the BCS scenario. The
superconductivity has been confirmed by magnetic susceptibility measurements
with Tc=203K. The high Tc superconductivity most likely is due to H3S which is
formed from H2S under its decomposition under pressure. Even higher Tc, room
temperature superconductivity, can be expected in other hydrogen-based
materials since hydrogen atoms provide the high frequency phonon modes as well
as the strong electron-phonon coupling. | 1506.08190v1 |
2014-05-01 | Effect of Electrical Properties on Gd modified BiFeO3-PbZrO3 | The 0.5(BiGdxFe1-xO3)-0.5(PbZrO3) composite was synthesized using a high
temperature solid-state reaction technique. Preliminary X-ray structural
analysis confirms the formation of the composite. The dielectric constant and
loss tangent have been studied. The hysteresis loop suggest that the material
is lossy. The impedance parameters were studied using an impedance analyzer in
a wide range of frequency (102-106 Hz) at different temperatures for all
samples. The Nyquist plot suggests the contribution of bulk effect as well as
grain boundary effect and the bulk resistance deceases with rise in temperature
for all samples. The electrical transport confirms the presence of hopping
mechanism in the material. The dc conductivity increases with rise in
temperature. The frequency variation of ac conductivity shows that the compound
obeys Jonschers universal power law and confirms the Small Polaron (SP)
tunneling effect due to low activation energy for all samples. Temperature
dependence of dc and ac conductivity indicates that electrical conduction in
the materials are thermally activated process. | 1405.0104v1 |
2019-02-13 | Cu-substituted Fe2P: An emerging candidates for magnetic RAM application | We propose that Cu-substituted Fe$_2$P, (Fe$_{1-x}$Cu$_x$)$_2$P ($x\sim
0.16$), to be an outstanding contender for the STT-MRAM application. Using
first principles based calculations in the framework of density functional
theory and through Monte Carlo simulations, we demonstrate that this material
can be used as ferromagnetic electrode in the magnetic tunnel junction (MTJ) of
STT-MRAM due to its moderate perpendicular magnetic anisotropy (PMA), large
tunnel magneto-resistance (TMR), good thermal stability and high ferromagnetic
transition temperature. We point out that the simplicity in the synthesis, huge
abundance, and non-toxicity make this material a very good candidate to replace
the current MTJ materials for STT-MRAM such as FePt,~FeCo or FeCoB. | 1902.04876v1 |
2012-06-01 | Novel highly conductive and transparent graphene based conductors | Future wearable electronics, displays and photovoltaic devices rely on highly
conductive, transparent and yet mechanically flexible materials. Nowadays
indium tin oxide (ITO) is the most wide spread transparent conductor in
optoelectronic applications, however the mechanical rigidity of this material
limits its use for future flexible devices. Here we report novel transparent
conductors based on few layer graphene (FLG) intercalated with ferric chloride
(FeCl3) with an outstandingly high electrical conductivity and optical
transparency. We show that upon intercalation a record low sheet resistance of
8.8 Ohm/square is attained together with an optical transmittance higher than
84% in the visible range. These parameters outperform the best values of ITO
and of other carbon-based materials, making these novel transparent conductors
the best candidates for future flexible optoelectronics. | 1206.0001v1 |
2020-11-16 | First-principles study of the electronic, magnetic, and crystal structure of perovskite molybdates | The molybdate oxides SrMoO$_3$, PbMoO$_3$, and LaMoO$_3$ are a class of
metallic perovskites that exhibit interesting properties including high
mobility, and unusual resistivity behavior. We use first-principles methods
based on density functional theory to explore the electronic, crystal, and
magnetic structure of these materials. In order to account for the electron
correlations in the partially-filled Mo $4d$ shell, a local Hubbard $U$
interaction is included. The value of $U$ is estimated via the constrained
random-phase approximation approach, and the dependence of the results on the
choice of $U$ are explored. For all materials, GGA+$U$ predicts a metal with an
orthorhombic, antiferromagnetic structure. For LaMoO$_3$, the $Pnma$ space
group is the most stable, while for SrMoO$_3$ and PbMoO$_3$, the $Imma$ and
$Pnma$ structures are close in energy. The $R_4^+$ octahedral rotations for
SrMoO$_3$ and PbMoO$_3$ are found to be overestimated compared to the
experimental low-temperature structure. | 2011.08323v2 |
2020-11-21 | Flash microwave pressing of zirconia | Microwave Pressing is a promising way to reduce microwave sintering
temperatures and stabilize microwave powder materials processing. A
multi-physics simulation was conducted of the regulated pressure-assisted
microwave cavity. This simulation took into consideration resonance phenomena
and the nonlinear temperature-dependent material parameters of zirconia. The
intrinsic behaviors of microwave systems and zirconia make the regulation of
the microwave pressing difficult. However, the same phenomena can be used to
activate flash sintering. Flash microwave sintering uses high electric fields
of the resonant microwave profile, the Negative Temperature Behavior (NTC) of
zirconia resistivity, and the mechanical pressure applied to the powder via a
die compaction configuration. The resulting flash microwave pressing still
needs improvement in terms of the processed material structure homogeneity, but
it has the capacity to become the fastest sintering treatment as it allows room
temperature activation where the total process time only takes a few seconds.
In addition, this 10-20s processing technique has shown good potential for
improving the transparency of alumina pre-sintered specimens. | 2011.14009v1 |
2021-03-28 | Acoustic-pressure-assisted engineering of aluminium foams | Foaming metals modulates their physical properties, enabling attractive
applications where lightweight, low thermal conductivity or acoustic isolation
are desirable. Adjusting the size of the bubbles in the foams is particularly
relevant for targeted applications. Here we provide a method with a detailed
theoretical understanding how to tune the size of the bubbles in aluminium
melts in-situ via acoustic pressure. Our description is in full agreement with
the high-rate three-dimensional X-Ray radioscopy of the bubble formation. We
complement our study with the intriguing results on the effect of foaming on
electrical resistivity, Seebeck coefficient and thermal conductivity from
cryogenic to room temperature. Compared to bulk materials the investigated foam
shows an enhancement in the thermoelectric figure of merit. These results
herald promising application of foaming in thermoelectrics materials and
devices for thermal energy conversion. | 2103.15225v1 |
2023-04-21 | Probabilistic selection and design of concrete using machine learning | Development of robust concrete mixes with a lower environmental impact is
challenging due to natural variability in constituent materials and a multitude
of possible combinations of mix proportions. Making reliable property
predictions with machine learning can facilitate performance-based
specification of concrete, reducing material inefficiencies and improving the
sustainability of concrete construction. In this work, we develop a machine
learning algorithm that can utilize intermediate target variables and their
associated noise to predict the final target variable. We apply the methodology
to specify a concrete mix that has high resistance to carbonation, and another
concrete mix that has low environmental impact. Both mixes also fulfill targets
on the strength, density, and cost. The specified mixes are experimentally
validated against their predictions. Our generic methodology enables the
exploitation of noise in machine learning, which has a broad range of
applications in structural engineering and beyond. | 2304.11226v1 |
2024-03-08 | Superconductivity of the New Medium-Entropy Alloy V4Ti2W with a Body-Centered Cubic Structure | Medium- and high-entropy alloy (MEA and HEA) superconductors have attracted
considerable interest since their discovery. This paper reports the
superconducting properties of ternary tungsten-containing MEA V4Ti2W for the
first time. V4Ti2W is a type II superconductor with a body-centered cubic (BCC)
structure. Experimental results of resistivity, magnetization, and heat
capacity indicate that the superconducting transition temperature of the MEA
V4Ti2W is roughly 5.0 K. The critical magnetic fields at the upper and lower
ends are 9.93(2) T and 40.7(3) mT, respectively. Interestingly, few BCC MEA
superconductors with VEC greater than 4.8 have been found. The addition of
tungsten leads to a VEC of 4.83 e/a for V4Ti2W, which is rarely higher than the
4.8 value. Adding tungsten element expands the variety of MEA alloys, which may
improve the microstructure and mechanical properties of materials and even
superconducting properties. This material could potentially offer a new
platform for the investigation of innovative MEA and HEA superconductors. | 2403.05115v1 |
2024-03-28 | Challenges in extracting nonlinear current-induced phenomena in Ca2RuO4 | An appealing direction to change the properties of strongly correlated
materials is to induce nonequilibrium steady states by the application of a
direct current. While access to these novel states is of high scientific
interest, Joule heating due to current flow often constitutes a hurdle to
identify nonthermal effects. The biggest challenge usually resides in measuring
accurately the temperature of a sample subjected to direct current, and to use
probes that give direct information of the material. In this work, we exploit
the simultaneous measurement of electrical transport and magnetisation to probe
non-equilibrium steady states in Ca2RuO4. In order to reveal non-thermal
current-induced effects, we employ a simple model of Joule self-heating to
remove the effects of heating and discuss the importance of temperature
inhomogeneity within the sample. Our approach provides a solid basis for
investigating current-induced phenomena in highly resistive materials. | 2403.19210v1 |
2000-01-07 | Near-Field Microwave Microscopy of Materials Properties | Near-field microwave microscopy has created the opportunity for a new class
of electrodynamics experiments of materials. Freed from the constraints of
traditional microwave optics, experiments can be carried out at high spatial
resolution over a broad frequency range. In addition, the measurements can be
done quantitatively so that images of microwave materials properties can be
created. We review the five major types of near-field microwave microscopes and
discuss our own form of microscopy in detail. Quantitative images of microwave
sheet resistance, dielectric constant, and dielectric tunability are presented
and discussed. Future prospects for near-field measurements of microwave
electrodynamic properties are also presented. | 0001075v2 |
2010-08-18 | A Stepped Oxide Hetero-Material Gate Trench Power MOSFET for Improved Performance | In this work, we propose a new Stepped Oxide Hetero-Material Trench (SOHMT)
power MOSFET with three sections in the trench gate (an N+ poly gate sandwiched
between two P+ poly gates) and having different gate oxide thicknesses
(increasing from source side to drain side). The different gate oxide thickness
serves the purpose of simultaneously achieving (i) a good gate control on the
channel charge and (ii) a lesser gate to drain capacitance. As a result, we
obtain higher transconductance as well as reduced switching delays, making the
proposed device suitable for both RF amplification and high speed switching
applications. In addition, the sandwiched gate with different work function
gate materials modifies the electric field profile in the channel resulting in
an improved breakdown voltage. Using two-dimensional simulations, we have shown
that the proposed device structure exhibits about 32% enhancement in breakdown
voltage, 25% reduction in switching delays, 20% enhancement in peak
transconductance and 10% reduction in figure of merit (product of ON-resistance
and gate charge) as compared to the conventional trench gate MOSFET. | 1008.3022v1 |
2016-10-05 | A Novel Nanoporous Graphite Based on Graphynes: First Principles Structure and Carbon Dioxide Preferential Physisorption | Ubiquitous graphene is a stricly 2D material representing an ideal adsorbing
platform due to its large specific surface area as well as its mechanical
strength and resistance to both thermal and chemical stresses. However,
graphene as a bulk material has the tendency to form irreversible agglomerates
leading to 3D graphitic structures with a significant decrease of the area
available for adsorption and no room for gas intercalation. In this paper a
novel nanoporous graphite formed by graphtriyne sheets is introduced: its 3D
structure is theoretically assessed by means of electronic structure and
molecular dynamics computations within the DFT level of theory. It is found
that the novel layered carbon allotrope is almost as compact as pristine
graphite but the inherent porosity of the 2D graphyne sheets and its relative
stacking leads to nanochannels that cross the material and whose sub-nanometer
size could allow the diffusion and storage of gas species. A molecular
prototype of the nanochannel is used to accurately determine first principles
adsorption energies and enthalpies for CO2, N2, H2O and H2 within the pores.
The proposed porous graphite presents no significant barrier for gas diffusion
and it shows a high propensity for CO2 physisorption with respect to the other
relevant components in both pre- and post-combustion gas streams. | 1610.01313v1 |
2017-06-30 | Role of anisotropy in determining stability of electrodeposition at solid-solid interfaces | We investigate the stability of electrodeposition at solid-solid interfaces
for materials exhibiting an anisotropic mechanical response. The stability of
electrodeposition or resistance to the formation of dendrites is studied within
a linear stability analysis. The deformation and stress equations are solved
using the Stroh formalism and faithfully recover the boundary conditions at the
interface. The stability parameter is used to quantify the stability of
different solid-solid interfaces incorporating the full anisotropy of the
elastic tensor of the two materials. Results show a high degree of variability
in the stability parameter depending on the crystallographic orientation of the
solids in contact, and point to opportunities for exploiting this effect in
developing Li metal anodes. | 1707.00064v3 |
2021-02-27 | van der Waals heterostructures based on atomically-thin superconductors | Van der Waals heterostructures (vdWHs) allow the assembly of high-crystalline
two-dimensional (2D) materials in order to explore dimensionality effects in
strongly correlated systems and the emergence of potential new physical
scenarios. In this work, it is illustrated the feasibility to integrate 2D
materials in-between 2D superconductors. Particularly, it is presented the
fabrication and electrical characterization of vertical vdWHs based on
air-unstable atomically-thin transition metal dichalcogenides formed by
NbSe2/TaS2/NbSe2 stacks, with TaS2 being the insulator 1T-TaS2 or the metal
2H-TaS2. Phase transitions as 1T-TaS2 charge density wave and NbSe2
superconductivity are detected. An enhancement of the vdWH resistance due to
Andreev reflections is observed below the superconducting transition
temperature of the NbSe2 flakes. Moreover, in the NbSe2 superconducting state,
the field and temperature dependence of the normalized conductance is analyzed
within the Dynes' model and the overall behavior is consistent with the
Bardeen-Cooper-Schrieffer theory. This vdWH approach can be extended to other
2D materials, such as 2D magnets or topological insulators, with the aim of
exploring the new emergent properties that may arise from such combinations. | 2103.00203v1 |
2022-11-18 | Pressure-Tuning Superconductivity in Noncentrosymmetric Topological Materials ZrRuAs | Recently, the hexagonal phase of ternary transition metal pnictides TT'X (T =
Zr, Hf; T'= Ru; X = P, As), which are well-known noncentrosymmetric
superconductors, were predicted to host nontrivial bulk topology. In this work,
we systematically investigate the electronic responses of ZrRuAs to external
pressure. At ambient pressure, ZrRuAs show superconductivity with Tc ~ 7.74 K,
while a large upper critical field ~ 13.03 T is obtained for ZrRuAs, which is
comparable to the weak-coupling Pauli limit. The resistivity of ZrRuAs exhibits
a non-monotonic evolution with increasing pressure. The superconducting
transition temperature Tc increases with applied pressure and reaches a maximum
value of 7.93 K at 2.1 GPa, followed by a decrease. The nontrivial topology is
robust and persists up to the high-pressure regime. Considering both robust
superconductivity and intriguing topology in this material, our results could
contribute to studies of the interplay between topological electronic states
and superconductivity. | 2211.10289v1 |
2023-03-28 | On optimization of heterogeneous materials for enhanced resistance to bulk fracture | We propose a novel approach to optimize the design of heterogeneous
materials, with the goal of enhancing their effective fracture toughness under
mode-I loading. The method employs a Gaussian processes-based Bayesian
optimization framework to determine the optimal shapes and locations of stiff
elliptical inclusions within a periodic microstructure in two dimensions. To
model crack propagation, the phase-field fracture method with an efficient
interior-point monolithic solver and adaptive mesh refinement, is used. To
account for the high sensitivity of fracture properties to initial crack
location with respect to heterogeneities, we consider multiple cases of initial
crack and optimize the material for the worst-case scenario. We also impose a
minimum clearance constraint between the inclusions to ensure design
feasibility. Numerical experiments demonstrate that the method significantly
improves the fracture toughness of the material compared to the homogeneous
case. | 2303.15801v1 |
2024-01-23 | Electronic Noise Spectroscopy of Quasi-2D van der Waals Antiferromagnetic Semiconductors | We investigated low-frequency current fluctuations, i.e. electronic noise, in
FePS3 van der Waals, layered antiferromagnetic semiconductor. The noise
measurements have been used as noise spectroscopy for advanced materials
characterization of the charge carrier dynamics affected by spin ordering and
trapping states. Owing to the high resistivity of the material, we conducted
measurements on vertical device configuration. The measured noise spectra
reveal pronounced Lorentzian peaks of two different origins. One peak is
observed only near the Neel temperature and it is attributed to the
corresponding magnetic phase transition. The second Lorentzian peak, visible in
the entire measured temperature range, has the characteristics of the
trap-assisted generation-recombination processes similar to those in
conventional semiconductors but shows a clear effect of the spin order
reconfiguration near the Neel temperature. The obtained results contribute to
understanding the electron and spin dynamics in this type of antiferromagnetic
semiconductors and demonstrate the potential of electronic noise spectroscopy
for advanced materials characterization. | 2401.12432v1 |
2015-04-24 | Graphene surpasses GaAs/AlGaAs for the application of the quantum Hall effect in metrology | The quantum Hall effect (QHE) theoretically provides a universal standard of
electrical resistance in terms of the Planck constant $h$ and the electron
charge $e$. In graphene, the spacing between the lowest discrete energy levels
occupied by the charge carriers under magnetic field is exceptionally large.
This is promising for a quantum Hall resistance standard more practical in
graphene than in the GaAs/AlGaAs devices currently used in national metrology
institutes. Here, we demonstrate that large QHE devices, made of high quality
graphene grown by propane/hydrogen chemical vapour deposition on SiC
substrates, can surpass state-of-the-art GaAs/AlGaAs devices by considerable
margins in their required operational conditions. In particular, in the device
presented here, the Hall resistance is accurately quantized within $1\times
10^{-9}$ over a 10-T wide range of magnetic field with a remarkable lower bound
at 3.5 T, temperatures as high as 10 K, or measurement currents as high as 0.5
mA. These significantly enlarged and relaxed operational conditions, with a
very convenient compromise of 5 T, 5.1 K and 50 $\mu$A, set the superiority of
graphene for this application and for the new generation of versatile and
user-friendly quantum standards, compatible with a broader industrial use. We
also measured an agreement of the quantized Hall resistance in graphene and
GaAs/AlGaAs with an ultimate relative uncertainty of $8.2\times 10^{-11}$. This
supports the universality of the QHE and its theoretical relation to $h$ and
$e$, essential for the application in metrology, particularly in view of the
forthcoming Syst\`eme International d'unit\'es (SI) based on fundamental
constants of physics, including the redefinition of the kilogram in terms of
$h$. | 1504.06511v1 |
2009-12-24 | Nanostructural Superconducting Materials for Fault Current Limiters and Cryogenic Electrical Machines | Materials of the Y-Ba-Cu-O (melt-textured YBa2Cu3O7-d-based materials or
MT-YBCO) and Mg-B-O (MgB2-based materials) systems with high superconducting
performance, which can be attained due to the formation of regularly
distributed nanostructural defects and inhomogenities in their structure can be
effectively used in cryogenic technique, in particular in fault current
limiters and electrical machines (electromotors, generators, pumps for liquid
gases, etc.). The developed processes of high-temperature (900-800 oC)
oxygenation under elevated pressure (16 MPa) of MT-YBCO and high-pressure (2
GPa) synthesis of MgB2-based materials allowed us to attain high SC (critical
current densities, upper critical fields, fields of irreversibility, trapped
magnetic fields) and mechanical (hardness, fracture toughness, Young modulus)
characteristics. It has been shown that the effect of materials properties
improvement in the case of MT-YBCO was attained due to the formation of high
twin density (20-22 micron-1), prevention of macrockracking and reduction (by a
factor of 4.5) of microcrack density, and in the case of MgB2-based materials
due to the formation of oxygen-enriched as compared to the matrix phase
fine-dispersed Mg-B-O inhomogenities as well as inclusions of higher borides
with near-MgB12 stoichiometry in the Mg-B-O matrix (with 15-37 nm average grain
sizes). The possibility is shown to obtain the rather high Tc (37 K) and
critical current densities in materials with MgB12 matrix (with 95 percent of
shielding fraction as calculated from the resistant curve). | 0912.4899v1 |
2010-11-01 | Modeling materials with optimized transport properties | Following demands for materials with peculiar transport properties, e.g. in
magnetoelectronics or thermoelectrics, there is a need for materials modeling
at the quantum-mechanical level. We combine density-functional with various
scale-bridging tools to establish correlations between the macroscopic
properties and the atomic structure of materials. For examples, magnetic memory
devices exploiting the tunneling magneto-resistance (TMR) effect depend
crucially on the spin polarization of the electrodes. Heusler alloys, e.g.
Co2MnSi, if perfectly ordered, are ferromagnetic half-metals with (ideally)
100% spin polarization. Their performance as electrodes in TMR devices is
limited by atomic disorder and deviations from perfect stoichiometry, but also
by interface states at the tunneling barrier. We use ab initio thermodynamics
in conjunction with the cluster expansion technique to show that excess
manganese in the alloy and at the interface helps to preserve the desired
half-metallic property. As another example, nanostructured materials with a
reduced thermal conductivity but good electrical conductivity are sought for
applications in thermoelectrics. Semiconductor heterostructures with a regular
arrangement of nanoscale inclusions ('quantum dot superlattices') hold the
promise of a high thermoelectric figure of merit. Our theoretical analysis
reveals that an increased figure of merit is to be expected if the quantum dot
size, the superlattice period and the doping level are all suitably fine-tuned.
Such a superlattice thus constitutes a material whose transport properties are
controlled by geometrical features at the nanoscale. | 1011.0324v1 |
2023-05-15 | Thermal conductivity of macroporous graphene aerogel measured using high resolution comparative infrared thermal microscopy | Graphene aerogel (GA) is a promising material for thermal management
applications across many fields due to its lightweight and thermally insulative
properties. However, standard values for important thermal properties, such as
thermal conductivity, remain elusive due to the lack of reliable
characterization techniques for highly porous materials. Comparative infrared
thermal microscopy (CITM) is an attractive technique to obtain thermal
conductance values of porous materials like GA, due to its non-invasive
character, which requires no probing of, or contact with, the often-delicate
structures and frameworks. In this study, we improve upon CITM by utilizing a
higher resolution imaging setup and reducing the need for pore-filling coating
of the sample (previously used to adjust for emissivity). This upgraded setup,
verified by characterizing porous silica aerogel, allows for a more accurate
confirmation of the fundamental thermal conductivity value of GA while still
accounting for the thermal resistance at material boundaries. Using this
improved method, we measure a thermal conductivity below 0.036 W/m$\cdot$K for
commercial GA using multiple reference materials. These measurements
demonstrate the impact of higher resolution thermal imaging to improve accuracy
in low density, highly porous materials characterization. This study also
reports thermal conductivity for much lower density (less than 15 mg/cm$^3$) GA
than previously published studies while maintaining the robustness of the CITM
technique. | 2305.09033v3 |
2024-04-18 | Assessing the Risk of Proliferation via Fissile Material Breeding in ARC-class Fusion Reactors | Construction of a nuclear weapon requires access to kilogram-scale quantities
of fissile material, which can be bred from fertile material like U-238 and
Th-232 via neutron capture. Future fusion power plants, with total neutron
source rates in excess of $10^{20}$ n/s, could breed weapons-relevant
quantities of fissile material on short timescales, posing a breakout
proliferation risk. The ARC-class fusion reactor design is characterized by
demountable high temperature superconducting magnets, a FLiBe liquid immersion
blanket, and a relatively small size ($\sim$ 4 m major radius, $\sim$ 1 m minor
radius). We use the open-source Monte Carlo neutronics code OpenMC to perform
self-consistent time-dependent simulations of a representative ARC-class
blanket to assess the feasibility of a fissile breeding breakout scenario. We
find that a significant quantity of fissile material can be bred in less than
six months of full power operation for initial fertile inventories ranging from
5 to 50 metric tons, representing a non-negligible proliferation risk. We
further study the feasibility of this scenario by examining other consequences
of fissile breeding such as reduced tritium breeding ratio, extra heat from
fission and decay heat, isotopic purity of bred material, and self-protection
time of irradiated blanket material. We also examine the impact of Li-6
enrichment on fissile breeding and find that it substantially reduces breeding
rate, motivating its use as a proliferation resistance tool. | 2404.12451v1 |
2022-01-10 | A theory for anisotropic magnetoresistance in materials with two vector order parameters | Anisotropic magnetoresistance (AMR) and related planar Hall resistance (PHR)
are ubiquitous phenomena of magnetic materials. Although the universal angular
dependences of AMR and PHR in magnetic polycrystalline materials with one order
parameter are well known, no similar universal relation for other class of
magnetic materials are known to date. Here I present a general theory of
galvanomagnetic effects in magnetic materials with two vector order parameters,
such as magnetic single crystals with a dominated crystalline axis or
polycrystalline non-collinear ferrimagnetic materials. It is shown that AMR and
PHR have a universal angular dependence. In general, both longitudinal and
transverse resistivity are non-reciprocal in the absence of inversion symmetry:
Resistivity takes different value when the current is reversed. Different from
simple magnetic polycrystalline materials where AMR and PHR have the same
magnitude, and $\pi/4$ out of phase, the magnitude of AMR and PHR of materials
with two vector order parameters are not the same in general, and the phase
difference is not $\pi/4$. Instead of $\pi$ periodicity of the usual AMR and
PHR, the periodicities of materials with two order parameters are $2\pi$. | 2201.03316v1 |
2003-11-04 | Resistive transition in $π$-junction superconductors | The resistivity behavior of inhomogeneous superconductors with random $\pi$
junctions, as in high-$T_c$ materials with d-wave symmetry, is studied by
numerical simulation of a three-dimensional XY spin glass model. Above a
concentration threshold of antiferromagnetic couplings, a resistive transition
is found in the chiral-glass phase at finite temperatures and the critical
exponents are determined from dynamic scaling analysis. The power-law exponent
for the nonlinear contribution found in recent resistivity measurements is
determined by the dynamic critical exponent of this transition. | 0311083v1 |
2004-07-28 | Universal behavior of giant electroresistance in epitaxial La0.67Ca0.33MnO3 thin films | We report a giant resistance drop induced by dc electrical currents in
La0.67Ca0.33MnO3 epitaxial thin films. Resistance of the patterned thin films
decreases exponentially with increasing current and a maximum drop shows at the
temperature of resistance peak Tp. Variation of resistance with current
densities can be scaled below and above Tp, respectively. This work can be
useful for the future applications of electroresistance. | 0407719v2 |
2005-06-17 | Experimental Evidence for Zero DC Resistance of Superconductors | Even after nearly a century of discovery of superconductivity, there has been
no direct experimental proof of the expected zero resistance of
superconductors. Indeed, it has been believed that it is impossible to
experimentally show that the resistance has fallen exactly to zero. In this
work we demonstrate that the dc resistivity of a superconducting material below
the transition temperature has to be exactly zero. | 0506426v2 |
2007-11-29 | Increase of Thermal Resistance Between a Nanostructure and a Surface due to Phonon Multireflections | The thermal resistance between a nanostructure and a half-body is calculated
in the framework of particle-phonons physics. The current models approximate
the nanostructure as a thermal bath. We prove that the multireflections of heat
carriers in the nanostructure significantly increase resistance in
contradiction with former predictions. This increase depends on the shape of
the nanostructure and the heat carriers mean free path only. We provide a
general and simple expression for the contact resistance and examine the
specific cases of nanowires and nanoparticles. | 0711.4718v1 |
2009-09-07 | Low-Temperature Resistivity Anomalies in Periodic Curved Surfaces | Effects of periodic curvature on the the electrical resistivity of corrugated
semiconductor films are theoretically considered. The presence of a
curvature-induced potential affects the motion of electrons confined to the
thin curved film, resulting in a significant resistivity enhancement at
specific values of two geometric parameters: the amplitude and period of the
surface corrugation. The maximal values of the two parameters in order to
observe the corrugation-induced resistivity enhancement in actual experiments
are quantified by employing existing material constants. | 0909.1135v1 |
2011-02-23 | Pt/Ti/Al2O3/Al tunnel junctions showing electroforming-free bipolar resistive switching behavior | We investigated electroforming-free bipolar resistive switching behavior in
Pt/Ti/Al2O3/Al tunnel junctions where the Al2O3 tunnel barrier was naturally
formed on Al in air. Various compliance current values for the junction's set
switching successfully lead to various resistance values in its low resistance
state, suggesting the possibility for multi-level-operation. A mechanism for
the bipolar switching is qualitatively discussed in terms of the modulation of
the tunnel barrier by the reactive Ti layer on top of the barrier. | 1102.4720v1 |
2013-05-09 | Electrostatic gating of metallic and insulating phases in SmNiO3 ultrathin films | The correlated electron system SmNiO3 exhibits a metal-insulator phase
transition at 130 {\deg}C. Using an ionic liquid as an electric double layer
(EDL) gate on three-terminal ultrathin SmNiO3 devices, we investigate gate
control of the channel resistance and transition temperature. Resistance
reduction is observed across both insulating and metallic phases with ~25%
modulation at room temperature. We show that resistance modulation is
predominantly due to electrostatic charge accumulation and not electrochemical
doping by control experiments in inert and air en-vironments. We model the
resistance behavior and estimate the accumulated sheet density (~1-2 x 10^14
cm^-2) and EDL capacitance (~12 {\mu}F/cm^2). | 1305.2111v1 |
2013-06-18 | Some features of anomalous conductivity of vinylene and vinyl chloride copolymer films | Manifestations of anomalous conductivity in polar dielectric films is
demonstrated for the first time on samples of copolymer of vinylene and vinyl
chloride, as was previously observed on modified PVC samples. On the base of
these experimental results important new insights into the physical sense of
traditionally used in these conditions specific resistivity indicators, both
volume and surface, should be replaced by transverse and longitudinal
resistance (according to polymer film surface) respectively, because the
specific resistivity of polymer composite does not permits to calculate as
usual the resistance of sample of arbitrary form.. | 1306.4127v1 |
2013-07-02 | The density of states of graphene underneath a metal electrode and its correlation with the contact resistivity | The density of states (DOS) of graphene underneath a metal is estimated
through a quantum capacitance measurement of the metal/graphene/SiO2/n+-Si
contact structure fabricated by a resist-free metal deposition process.
Graphene underneath Au maintains a linear DOS - energy relationship except near
the Dirac point, whereas the DOS of graphene underneath Ni is broken and
largely enhanced around the Dirac point, resulting in only a slight modulation
of the Fermi energy. Moreover, the DOS of graphene in the contact structure is
correlated with the contact resistivity measured using devices fabricated by
the resist-free process. | 1307.0690v1 |
2013-08-06 | Correct nonlinearity and hysteresis of volt-ampere characteristics of spin valves, magnetic tunnel junctions and memristors | There are essential achievements in synthesis of interesting for creation of
compact electronic memory switched by own current structures of spin valves and
magnetic tunnel junctions with hysteretic current dependences of resistance. In
the offered message the attention to discrepancy to physical principles of a
hysteresis of resistance represented in publications is paid. It is
schematically presented how the dependences of resistance on current should
look not contradicting the energy conservation law for hysteresis dependence of
resistance on current and corresponding volt-ampere characteristic. | 1308.1220v1 |
2015-09-28 | Multi-level Resistive Switching Characteristics of W/Co:TiO2/FTO Structures | In the present work, multi-level resistive switching (RS) in W/Co:TiO2/FTO
structures induced by a multi-mixed mechanism was studied. It was found that
the devices could be reproducibly programmed into three nonvolatile resistance
states. And the directly switching between any resistance states was realized.
This increases the operation speed and lowers the complexity of control circuit
of multi-state nonvolatile memory. | 1509.08211v1 |
2020-09-16 | The electric pulses induced multi-resistance states in the hysteresis temperature range of 1T-TaS2 and 1T-TaS1.6Se0.4 | The electric pulse-induced responses of 1T-TaS2 and 1T-TaS1.6Se0.4 crystals
in the commensurate charge-density-wave (CCDW) phase in the hysteresis
temperature range have been investigated. We observed that abrupt multiple
steps of the resistance are excited by electric pulses at a fixed temperature
forming multi metastable like states. We propose that the response of the
system corresponds to the rearrangements of the textures of CCDW domains and
the multi-resistance states or the nonvolatile resistance properties excited
simply by electric pulses have profound significance for the exploration of
solid-state devices. | 2009.07587v1 |
2012-01-26 | Resistive switching effects on the spatial distribution of phases in metal-complex oxide interfaces | In order to determine the key parameters that control the resistive switching
mechanism in metal-complex oxides interfaces, we have studied the electrical
properties of metal / YBa2Cu3O7-d (YBCO) interfaces using metals with different
oxidation energy and work function (Au, Pt, Ag) deposited by sputtering on the
surface of a YBCO ceramic sample. By analyzing the IV characteristics of the
contact interfaces and the temperature dependence of their resistance, we
inferred that ion migration may generate or cancel conducting filaments, which
modify the resistance near the interface, in accordance with the predictions of
a recent model. | 1201.5670v1 |
2019-08-21 | Artificial Spin Ice Phase-Change Memory Resistors | We study the implications of the anisotropic magnetic resistance on permalloy
nanowires, and in particular on the property of the resistance depending on the
type of lattice. We discuss how the internal spin configuration of artificial
spin ice nanowires can affect their effective resistive state, and which
mechanisms can introduce a current-dependent effect dynamic resistive state. We
discuss a spin-induced thermal phase-change mechanism, and an athermal
domain-wall spin inversion. In both cases we observe memory behavior
reminiscent of a memristor, with an I-V hysteretic pinched behavior. | 1908.08073v1 |
2020-07-09 | Modeling Resistive Switching in Nanogranular Metal Films | Films produced by assembling bare gold clusters well beyond the electrical
percolation threshold show a resistive switching behavior whose investigation
has started only recently. Here we address the challenge to charaterize the
resistance of a nanogranular film starting from limited information on the
structure at the microscopic scale by the means of Bruggeman's approach to
multicomponent media, within the framework of Effective Medium Approximations.
The approach is used to build a model that proves that the observed resistive
switching can be explained by thermally regulated local structural
rearrangements. | 2007.04710v2 |
2019-01-12 | Development of the Micro Pixel Chamber with resistive electrodes | We developed a novel design of a Micro Pixel Chamber ($\mu$-PIC) with
resistive electrodes for a charged-particle-tracking detector in high-rate
applications. Diamond-Like Carbon (DLC) thin film is used for the cathodes. The
resistivity can be controlled flexibly ($\mathrm{10^{5-7}k\Omega/sq.}$) at high
uniformity. The fabrication-process was greatly improved and the resistive
$\mu$-PIC could be operated at 10$\times$10 $\mathrm{cm^2}$. Resistors for the
HV bias and capacitors for the AC coupling were completely removed by applying
PCB and carbon-sputtering techniques, and the resistive $\mu$-PIC became a very
compact detector. The performances of our new resistive $\mu$-PIC were measured
in various ways. Consequently, it was possible to attain high gas gains
($\mathrm{> 10^{4}}$), high detection efficiency, and position resolution
exceeding 100 $\mu$m. The spark current was suppressed, and the new resistive
$\mu$-PIC was operated stably under fast-neutrons irradiation. These features
offer solutions for a charged-particle-tracking detector in future high-rate
applications. | 1901.03836v1 |
2015-10-13 | Interface-mediated thermomechanical effects during high velocity impact between monocrystalline surfaces | High velocity impact between crystalline surfaces is important for a range of
material phenomena, yet a fundamental understanding of the effect of surface
structure, energetics and kinetics on the underlying thermo-mechanical response
remains elusive. Here, we employ non-equilibrium molecular dynamics (NEMD)
simulations to describe the nanoscale dynamics of the high velocity impact
between commensurate and incommensurate monocrystalline (001) copper surfaces.
For impact velocities in the range 100-1200 m/s, the kinetic energy dissipation
involves nucleation and emission of dislocation loops from defective sites
within the rapidly forming interface, well below the bulk single-crystal yield
point. At higher velocities, adiabatic dissipation occurs via
plasticity-induced heating as the interface structurally melts following the
impact. The adhesive strength of the reformed interface is controlled by the
formation and nucleation of dislocations and point defects as they modify the
interfacial energy relative to the deformed bulk. As confirmation, the excess
interface energy decreases monotonically with increasing impact velocity. The
relative crystal orientation of the surfaces equally important; the grain
boundaries formed following incommensurate impact exhibit higher impact
resistance, with smaller defect densities and interfacial enthalpies,
suggesting an enhanced ability of the grain boundaries to absorb the
non-equilibrium damage and therefore facilitate particle bonding. Our study
highlights the key role played by the atomic-scale surface structure in
determining the impact resistance and adhesion of crystalline surfaces. | 1510.03775v1 |
2007-10-03 | Directional-dependent thermally activated motion of vortex bundles and theory of anomalous Hall effect in type-II conventional and high-Tc superconductors | The anomalous Hall effect for type-II conventional and high-Tc
superconductors is studied based upon the theory of thermally activated motion
of vortex bundles jumping over the directional-dependent energy barrier. It is
shown that the Hall anomaly is universal for type-II conventional and high-Tc
superconductors as well as for superconducting bulk materials and thin films,
provided certain conditions are satisfied. We find that the
directional-dependent potential barrier of the vortex bundles renormalizes the
Hall and longitudinal resistivities, and Hall anomaly for superconductors is
induced by the competition between the Magnus force and the random collective
pinning force of the vortex bundle. We also find that the domain of anomalous
Hall effect includes two regions: the region of thermally activated motion of
the small vortex bundles and that of the large vortex bundles separated by the
contour of the quasiorder-disorder first-order phase transition, or the peak
effect of the vortex system. The Hall and longitudinal resistivities as
functions of temperature as well as applied magnetic field have been calculated
for type-II superconducting films and bulk materials. The conditions for
occurring the double sign reversal or reentry phenomenon is also investigated.
All the results are in agreement with the experiments. | 0710.0700v2 |
2022-04-20 | Superconducting bimodal ionic photo-memristor | Memristive circuit elements constitute a cornerstone for novel electronic
applications, such as neuromorphic computing, called to revolutionize
information technologies. By definition, memristors are sensitive to the
history of electrical stimuli, to which they respond by varying their
electrical resistance across a continuum of nonvolatile states. Recently, much
effort has been devoted to developing devices that present an analogous
response to optical excitation. Here we realize a new class of device, a
tunnelling photo-memristor, whose behaviour is bimodal: both electrical and
optical stimuli can trigger the switching across resistance states in a way
determined by the dual optical-electrical history. This unique behaviour is
obtained in a device of ultimate simplicity: an interface between a
high-temperature superconductor and a transparent semiconductor. The
microscopic mechanism at play is a reversible nanoscale redox reaction between
both materials, whose oxygen content determines the electron tunnelling rate
across their interface. Oxygen exchange is controlled here via illumination by
exploiting a competition between electrochemistry, photovoltaic effects and
photo-assisted ion migration. In addition to their fundamental interest, the
unveiled electro-optic memory effects have considerable technological
potential. Especially in combination with high-temperature superconductivity
which, beyond facilitating the high connectivity required in neuromorphic
circuits, brings photo-memristive effects to the realm of superconducting
electronics. | 2204.09255v1 |
2018-11-03 | Modern Data Analytics Approach to Predict Creep of High-Temperature Alloys | A breakthrough in alloy design often requires comprehensive understanding in
complex multi-component/multi-phase systems to generate novel material
hypotheses. We introduce a modern data analytics workflow that leverages
high-quality experimental data augmented with advanced features obtained from
high-fidelity models. Herein, we use an example of a consistently-measured
creep dataset of developmental high-temperature alloy combined with scientific
alloy features populated from a high-throughput computational thermodynamic
approach. Extensive correlation analyses provide ranking insights for most
impactful alloy features for creep resistance, evaluated from a large set of
candidate features suggested by domain experts. We also show that we can
accurately train machine learning models by integrating high-ranking features
obtained from correlation analyses. The demonstrated approach can be extended
beyond incorporating thermodynamic features, with input from domain experts
used to compile lists of features from other alloy physics, such as diffusion
kinetics and microstructure evolution. | 1811.01239v1 |
2021-01-24 | Electronic structure and transport properties of sol-gel-derived high-entropy Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3 thin films | High-entropy perovskite thin films, as the prototypical representative of the
high-entropy oxides with novel electrical and magnetic features, have recently
attracted great attention. Here, we reported the electronic structure and
charge transport properties of sol-gel-derived high-entropy
Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3 thin films annealed at various temperatures. By
means of X-ray photoelectron spectroscopy and absorption spectrum, it is found
that the conduction-band-minimum shifts downward and the valence-band-maximum
shifts upward with the increase of annealing temperature, leading to the
narrowed band gap. Electrical resistance measurements confirmed a
semiconductor-like behavior for all the thin films. Two charge transport
mechanisms, i.e., the thermally-activated transport mechanism at high
temperatures and the activation-less transport mechanism at low temperatures,
are identified by a self-consistent analysis method. These findings provide a
critical insight into the electronic band structure and charge transport
behavior of Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, validating it as a compelling
high-entropy oxide material for future electronic/energy-related technologies. | 2101.09633v2 |
2015-06-16 | Unforeseen high temperature and humidity stability of FeCl$_3$ intercalated few layer graphene | We present the first systematic study of the stability of the structure and
electrical properties of FeCl$_3$ intercalated few-layer graphene to high
levels of humidity and high temperature. Complementary experimental techniques
such as electrical transport, high resolution transmission electron microscopy
and Raman spectroscopy conclusively demonstrate the unforeseen stability of
this transparent conductor to a relative humidity up to $100 \%$ at room
temperature for 25 days, to a temperature up to $150\,^\circ$C in atmosphere
and up to a temperature as high as $620\,^\circ$C in vacuum, that is more than
twice higher than the temperature at which the intercalation is conducted. The
stability of FeCl$_3$ intercalated few-layer graphene together with its unique
values of low square resistance and high optical transparency, makes this
material an attractive transparent conductor in future flexible electronic
applications. | 1506.04907v1 |
2009-12-24 | Properties of MgB2 bulk | The review considers bulk MgB2-based materials in terms of their structure,
superconducting and mechanical properties. Superconducting transition
temperatures of 34.5-39.4 K, critical current densities of 1.8-1.0 x E6 A/sq.cm
in self field and 103 in 8 T field at 20 K, 3-1.5xE5 A/sq. cm in self field at
35 K, HC2 15 T at 22 K and Hirr 13 T at 20 K have been registered for
polycrystalline materials. As TEM and SEM study show, dispersed higher borides
and rather big amount (5-14 percents) of oxygen (bonded simultaneously with Mg
and B) can be present in the structure even if X-ray pattern contains only
reflexes of well crystallized MgB2 with traces of MgO. Materials with such a
rather high oxygen content demonstrated high superconducting characteristics.
At present it is established that nanosized MgB12 grains provide effective
pinning in polycrystalline material. Besides, additions can introduce the MgB2
structure inducing disorder in lattice sites (for example, C substitution for
B). The disorder increases the normal state resistivity, magnetic penetration
depth, and the upper critical field, but reduces the transition temperature and
anisotropy. It is highly probable that the additives (Ti, Ta, Zr, SiC) together
with synthesis or sintering temperature can affect the distribution of oxygen
and hydrogen in the material structure as well as the formation of grains of
higher borides, thus influencing superconducting properties. The
superconductivity of materials with matrix close to MgB12 in stoichiometry
(Tc=37 K) has been defined. | 0912.4906v1 |
2017-10-23 | Realization of a hole-doped Mott insulator on a triangular silicon lattice | The physics of doped Mott insulators is at the heart of some of the most
exotic physical phenomena in materials research including insulator-metal
transitions, colossal magneto-resistance, and high-temperature
superconductivity in layered perovskite compounds. Advances in this field would
greatly benefit from the availability of new material systems with similar
richness of physical phenomena, but with fewer chemical and structural
complications in comparison to oxides. Using scanning tunneling microscopy and
spectroscopy, we show that such a system can be realized on a silicon platform.
Adsorption of one-third monolayer of Sn atoms on a Si(111) surface produces a
triangular surface lattice with half-filled dangling bond orbitals. Modulation
hole-doping of these dangling bonds unveils clear hallmarks of Mott physics,
such as spectral weight transfer and the formation of quasi-particle states at
the Fermi level, well-defined Fermi contour segments, and a sharp singularity
in the density of states. These observations are remarkably similar to those
made in complex oxide materials, including high-temperature superconductors,
but highly extraordinary within the realm of conventional sp-bonded
semiconductor materials. It suggests that exotic quantum matter phases can be
realized and engineered on silicon-based materials platforms. | 1710.08065v1 |
2020-04-12 | Investigation on the Mechanical Properties of Functionally Graded Nickel and Aluminium Alloy by Molecular Dynamics Study | Functionally graded materials (FGMs), have drawn considerable attention of
the worldwide researchers and scientific community because of its unique
mechanical, thermal and electrical properties which may be exploited by varying
the compositions gradually over volume. This makes FGM multifunctional material
(properties changing continuously in a certain direction) for specific purpose
without creating any phase interface thus making it superior to its composite
counterparts. In this paper, we applied Molecular Dynamics (MD) approach to
investigate the mechanical properties of functional graded Ni-Al alloy with Ni
coating by applying uniaxial tension. Nickel-Aluminum (Ni-Al) alloy has been
used extensively in the industry due to its remarkable mechanical and thermal
properties. Our aim is to find the difference in material behavior when we
change the grading function (linear, elliptical and parabolic), temperature and
crystallographic direction. We also observe distinct type of failure mechanism
for different grading function at different temperature. Close observation
reveals that elliptically graded Ni-Al alloy has high tensile strength at low
temperature whereas at high temperature, the highest tensile strength is found
for parabolic grading. Besides, at any temperature, the parabolically graded
Ni-Al alloy shows superior elasticity than its elliptical and linear
counterpart. Moreover, it is also observed that [111] crystallographic
direction for this alloy demonstrates more resistivity towards failure than any
other crystallographic direction. It is found that lattice disorder plays a
significant role on the mechanical properties of Functionally Graded Materials
(FGMs). This paper details a pathway to tune the mechanical properties like
Young's Modulus, plasticity and yield strength at molecular level by varying
the composition of materials along different grading functions. | 2004.05651v1 |
1997-03-03 | Longitudinal and transverse dissipation in a simple model for the vortex lattice with screening | Transport properties of the vortex lattice in high temperature
superconductors are studied using numerical simulations in the case in which
the non-local interactions between vortex lines are dismissed. The results
obtained for the longitudinal and transverse resistivities in the presence of
quenched disorder are compared with the results of experimental measurements
and other numerical simulations where the full interaction is considered. This
work shows that the dependence on temperature of the resistivities is well
described by the model without interactions, thus indicating that many of the
transport characteristics of the vortex structure in real materials are mainly
a consequence of the topological configuration of the vortex structure only. In
addition, for highly anisotropic samples, a regime is obtained where
longitudinal coherence is lost at temperatures where transverse coherence is
still finite. I discuss the possibility of observing this regime in real
samples. | 9703035v1 |
1997-08-19 | Metallization of Fluid Hydrogen | The electrical resistivity of liquid hydrogen has been measured at the high
dynamic pressures, densities and temperatures that can be achieved with a
reverberating shock wave. The resulting data are most naturally interpreted in
terms of a continuous transition from a semiconducting to a metallic, largely
diatomic fluid, the latter at 140 GPa, (ninefold compression) and 3000 K. While
the fluid at these conditions resembles common liquid metals by the scale of
its resistivity of 500 micro-ohm-cm, it differs by retaining a strong pairing
character, and the precise mechanism by which a metallic state might be
attained is still a matter of debate. Some evident possibilities include (i)
physics of a largely one-body character, such as a band-overlap transition,
(ii) physics of a strong-coupling or many-body character,such as a Mott-Hubbard
transition, and (iii) processes in which structural changes are paramount. | 9708144v1 |
1997-09-16 | The Metallic-Like Conductivity of a Two-Dimensional Hole System | We report on a zero magnetic field transport study of a two-dimensional,
variable-density, hole system in GaAs. As the density is varied we observe, for
the first time in GaAs-based materials, a crossover from an insulating behavior
at low-density, to a metallic-like behavior at high-density, where the metallic
behavior is characterized by a large drop in the resistivity as the temperature
is lowered. These results are in agreement with recent experiments on Si-based
two-dimensional systems by Kravchenko et al. and others. We show that, in the
metallic region, the resistivity is dominated by an exponential
temperature-dependence with a characteristic temperature which is proportional
to the hole density, and appear to reach a constant value at lower
temperatures. | 9709184v3 |
1998-04-23 | Hysteretic behavior and evidence for domain formation in a double-layer quantum Hall system at total filling factor 2 | We report anomalous behavior in a double-layer two dimensional hole gas
(2DHG) at even integer filling factors which includes hysteresis in the
longitudinal and Hall resistances and a very weak temperature dependence of the
resistance minima. All anomalies disappear and the conventional quantum Hall
effect behavior recovers when a thin metal film is placed on top of the 2DHG.
The behavior is attributed to presence of the theoretically predicted magnetic
ordering at even integer filling factors which causes the formation of
macroscopic spin-charge domains. | 9804256v2 |
1998-11-18 | Hall-effect in LuNi_2B_2C in normal and superconducting mixed states | The Hall resistivity rho_{xy} of LuNi_2B_2C is negative in the normal as well
as in the mixed state and has no sign reversal typical for high-T_c
superconductors. A distinct nonlinearity in the rho_{xy} dependence on field H
was found in the normal state for T < 40K, accompanied by a large
magnetoresistance reaching +90% for mu_0H=16T at T=20K. The scaling relation
rho_{xy} ~ \rho_{xx}^\beta (\rho_{xx} is the longitudinal resistivity) was
found in the mixed state, the value of \beta being dependent on the degree of
disorder. | 9811273v1 |
1999-07-22 | Charge carrier density collapse in La_0.67Ca_0.33MnO_3 and La_0.67Sr_0.33MnO_3 epitaxial thin films | We measured the temperature dependence of the linear high field Hall
resistivity of La_0.67Ca_0.33MnO_3 (T_C=232K) and La_0.67Sr_0.33MnO_3
(T_C=345K) thin films in the temperature range from 4K up to 360K in magnetic
fields up to 20T. At low temperatures we find a charge carrier density of 1.3
and 1.4 holes per unit cell for the Ca- and Sr-doped compound, respectively. In
this temperature range electron-magnon scattering contributes to the
longitudinal resistivity. At the ferromagnetic transition temperature T_C a
dramatic drop in the number of current carriers $n$ down to 0.6 holes per unit
cell, accompanied by an increase in unit cell volume, is observed. Corrections
of the Hall data due to a non saturated magnetic state will lead a more
pronounced charge carrier density collapse. | 9907346v1 |
1999-08-05 | Fermi-level alignment at metal-carbon nanotube interfaces: application to scanning tunneling spectroscopy | At any metal-carbon nanotube interface there is charge transfer and the
induced interfacial field determines the position of the carbon nanotube band
structure relative to the metal Fermi-level. In the case of a single-wall
carbon nanotube (SWNT) supported on a gold substrate, we show that the charge
transfers induce a local electrostatic potential perturbation which gives rise
to the observed Fermi-level shift in scanning tunneling spectroscopy (STS)
measurements. We also discuss the relevance of this study to recent experiments
on carbon nanotube transistors and argue that the Fermi-level alignment will be
different for carbon nanotube transistors with low resistance and high
resistance contacts. | 9908073v3 |
1999-08-25 | Hall effect of epitaxial double-perovskite Sr_2FeMoO_6 thin films | We prepared high epitaxial thin films of the compound Sr_2FeMoO_6 with narrow
rocking curves by pulsed laser deposition. The diagonal and nondiagonal
elements of the resistivity tensor were investigated at temperatures from 4 K
up to room temperature in magnetic fields up to 8 T. An electronlike ordinary
Hall effect and a holelike anomalous Hall contribution are observed. Both
coefficients have reversed sign compared to the colossal magnetoresistive
manganites. We found at 300 K an ordinary Hall coefficent of -1.87x10^{-10}
m^3/As, corresponding to a nominal charge carrier density of four electrons per
formula unit. At low temperature only a small negative magnetoresistance is
observed which vanishes at higher temperatures. The temperature coefficient of
the resistivity is negative over the whole temperature range. A Kondo like
behavior is observed below 30 K while above 100 K variable range hopping like
transport occurs. | 9908361v2 |
1999-10-15 | Electronic Transport in a Three-dimensional Network of 1-D Bismuth Quantum Wires | The resistance R of a high density network of 6 nm diameter Bi wires in
porous Vycor glass is studied in order to observe its expected semiconductor
behavior. R increases from 300 K down to 0.3 K. Below 4 K, where R varies
approximately as ln(1/T), the order-of-magnitude of the resistance rise, as
well as the behavior of the magnetoresistance are consistent with localization
and electron-electron interaction theories of a one-dimensional disordered
conductor in the presence of strong spin-orbit scattering. We show that this
behaviour and the surface-enhanced carrier density may mask the proposed
semimetal-to-semiconductor transition for quantum Bi wires. | 9910241v1 |
2000-01-25 | Pressure Induced Quantum Critical Point and Non-Fermi-Liquid Behavior in BaVS3 | The phase diagram of BaVS3 is studied under pressure using resistivity
measurements. The temperature of the metal to nonmagnetic Mott insulator
transition decreases under pressure, and vanishes at the quantum critical point
p_cr=20kbar. We find two kinds of anomalous conducting states. The
high-pressure metallic phase is a non-Fermi liquid described by Delta rho = T^n
where n=1.2-1.3 at 1K < T < 60K. At p<p_cr, the transition is preceded by a
wide precursor region with critically increasing resistivity which we ascribe
to the opening of a soft Coulomb gap. | 0001371v2 |
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