publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2000-03-14 | Magnetic and electrical resistance behaviour of the oxides, Ca$_{3-x}$Y$_x$LiRuO$_6$ (x= 0.0, 0.5 and 1.0) | We have investigated the magnetic and electrical resistance behaviour of
Ca$_{3-x}$Y$_x$LiRuO$_6$. The parent compound exhibits magnetic ordering from
Ru sublattice at a rather high temperature, 113 K. Though the paramagnetic
Curie temperature ($\theta$$_p$) is negative indicative of antiferromagnetic
ordering, the large magnitude (-250 K) of $\theta$$_p$ reveals complex nature
of the magnetism in this compound. Ru ions appear to be in the pentavalent
state. We note that the N\'eel temperature undergoes only a marginal reduction
by Y substitution. All these compositions are found to be insulators and thus
the electron doping does not result in metallicity. Thus the overall magnetic
and transport behaviour are found to be essentially insensitive to Y
substitution for Ca, a finding which may favour the idea of
quasi-one-dimensional magnetism in these compounds. | 0003227v1 |
2001-03-26 | Superconducting Mg-B films by pulsed laser deposition in an in-situ two-step process using multi-component targets | Superconducting thin films have been prepared in a two-step in-situ process,
using the Mg-B plasma generated by pulsed laser ablation. The target was
composed of a mixture of Mg and MgB2 powders to compensate for the volatility
of Mg and therefore to ensure a high Mg content in the film. The films were
deposited at temperatures ranging from room temperature to 300 degrees C
followed by a low-pressure in-situ annealing procedure. Various substrates have
been used and diverse ways to increase the Mg content into the film were
applied. The films show a sharp transition in the resistance and have a zero
resistance transition temperature of 22-24 K. | 0103543v1 |
2001-05-29 | Growth, structure analysis and anisotropic superconducting properties of MgB2 single crystals | Here we report the growth of sub-millimeter MgB2 single crystals of various
shapes under high pressure in Mg-B-N system. Structure refinement using a
single-crystal X-ray diffraction analysis gives lattice parameters a=3.0851(5)
A and c=3.5201(5) A with small reliability factors (Rw =0.025, R=0.018), which
enables us to analyze the Fourier and Fourier difference maps. The maps clearly
show the B sp2 orbitals and covalency of the B-B bonds. The sharp
superconducting transitions at Tc =38.1-38.3K were obtained in both
magnetization (DTc =0.6K) and resistivity (DTc <0.3K) measurements. Resistivity
measurements with magnetic fields applied parallel and perpendicular to the Mg
and B sheets reveal the anisotropic nature of this compound, with upper
critical field anisotropy ratio of about 2.7. | 0105545v2 |
2001-10-18 | Strong Quasiparticle Trapping In A 6x6 Array Of Vanadium-Aluminum Superconducting Tunnel Junctions | A 6x6 array of symmetrical V/Al/AlOx/Al/V Superconducting Tunnel Junctions
(STJs) was fabricated. The base electrode is a high quality epitaxial film with
a residual resistance ratio (RRR) of ~30. The top film is polycrystalline with
an RRR of ~10. The leakage currents of the 25x25 mm^2 junctions are of the
order of 0.5 pA/mm^2 at a bias voltage of 100 mV, which corresponds to a
dynamical resistance of ~ 3 10^5 ohms. When the array was illuminated by 6 keV
X-ray photons from a 55Fe radioactive source the single photon charge output
was found to be low and strongly dependent on the temperature of the devices.
This temperature dependence at X-ray energies can be explained by the existence
of a very large number of quasiparticle (QP) traps in the Vanadium. QPs are
confined in these traps, having a lower energy gap than the surrounding
material, and are therefore not available for tunneling. The number of traps
can be derived from the energy dependence of the responsivity of the devices
(charge output per electron volt of photon input energy). | 0110374v1 |
2001-10-18 | Magnetic and transport properties of the new antiferromagnetic Kondo-lattice CeNiBi2 | We report results of the first studies on the magnetic and transport
properties of a new material CeNiBi_2. The magnetic susceptibility exhibits a
sharp peak at T_N = 6K, indicating an antiferromagnetic phase transition. This
antiferromagnetic order below T_N is confirmed by magnetization measurement,
which displays a metamagnetic-like transition at H_m = 5 T. Both
low-temperature susceptibility and high-field magnetization are suggestive of
strong crystalline-electric-field effect in CeNiBi_2. The electrical
resistivity shows the presence of Kondo and crystal-field effects with a sharp
drop below TN due to the antiferromagnetic ordering. This sharp drop below T_N
in the electrical resistivity is suppressed slightly to higher temperatures by
an applied magnetic field to 18 T. With increasing magnetic field, the slope of
magnetoresistance changes from positive to negative, being indicative of the
transition to a ferromagnetic state. | 0110380v1 |
2002-03-08 | Strain effect on electronic transport and ferromagnetic transition temperature in La$_{0.9}$Sr$_{0.1}$MnO$_{3}$ thin films | We report on a systematic study of strain effects on the transport properties
and the ferromagnetic transition temperature $T_{c}$ of high-quality
La$_{0.9}$Sr$_{0.1}$MnO$_{3}$ thin films epitaxially grown on (100) SrTiO$_{3}$
substrates. Both the magnetization and the resistivity are critically dependent
on the film thickness. $T_{c}$ is enhanced with decreasing the film thickness
due to the compressive stain produced by lattice mismatch. The resistivity
above 165 K of the films with various thicknesses is consistent with small
polaronic hopping conductivity. The polaronic formation energy $E_{P}$ is
reduced with the decrease of film thickness. We found that the strain
dependence of $T_{c}$ mainly results from the strain-induced electron-phonon
coupling. The strain effect on $E_{P}$ is in good agreement with the
theoretical predictions. | 0203196v1 |
2002-04-22 | Role of Umklapp Processes in Conductivity of Doped Two-Leg Ladders | Recent conductivity measurements performed on the hole-doped two-leg ladder
material $\mathrm{Sr_{14-x}Ca_xCu_{24}O_{41}}$ reveal an approximately linear
power law regime in the c-axis DC resistivity as a function of temperature for
$x=11$. In this work, we employ a bosonic model to argue that umklapp processes
are responsible for this feature and for the high spectral weight in the
optical conductivity which occurs beyond the finite frequency Drude-like peak.
Including quenched disorder in our model allows us to reproduce experimental
conductivity and resistivity curves over a wide range of energies. We also
point out the differences between the effect of umklapp processes in a single
chain and in the two-leg ladder. | 0204485v1 |
2002-07-02 | Comment to the paper : Collapse of the vortex-lattice inductance and shear modulus at the melting transition in untwinned YBa$_2$Cu$_3$O$_7$, by Matl \QTR{em}{et al.} | In a recent paper, Matl et al present a high-frequency study of the complex
resistivity of a pinned vortex lattice in YBaCuO . They focus on the
inductive-to-resistive transition which is investigated as a function of
temperature at a constant field $B_0=2$ T, so that the transition is associated
with the vanishing of vortex pinning strength. To our view, their conclusions
rely on a rather brittle experimental body and the collapse of C66 results from
an involved analysis of the finite frequency corrections to $\rho (\omega)$.
These corrections are not necessary since the complex frequency spectrum has
been previously interpreted by the two modes model, first proposed for low Tc
materials. We think that it is more adequate to interpret the present data and
should be at least considered. | 0207074v1 |
2003-05-21 | Carbon-substituted MgB2 single crystals | Carbon-substituted MgB2 single crystals, Mg(B_1-xC_x)_2 of 0.3-1.0 mm size
were grown for x=0.02-0.15 by a high-pressure technique. The doping dependence
of lattice constants studied in a range of x=0.0-0.2 shows a monotonic decrease
in a, while the c parameter remains almost invariant. Using X-ray diffraction
and Auger electron spectroscopy, the solubility limit of C in MgB2 was
estimated to be about 15(+/-)1%,which is substantially larger than that
reported for the polycrystalline samples synthesized by encapsulation
techniques. Measurements of temperature dependence of magnetization and
resistivity showed a dramatic decrease in Tc with C-substitution, followed by
complete suppression of superconductivity for x>0.125. Resistivity measurements
in magnetic fields parallel and perpendicular to the basal plane of the
crystals showed a nearly isotropic state in the heavily-doped crystals (x>0.1). | 0305485v1 |
2003-07-01 | Efficient nonlinear room-temperature spin injection from ferromagnets into semiconductors through a modified Schottky barrier | We suggest a consistent microscopic theory of spin injection from a
ferromagnet (FM) into a semiconductor (S). It describes tunneling and emission
of electrons through modified FM-S Schottky barrier with an ultrathin heavily
doped interfacial S layer . We calculate nonlinear spin-selective properties of
such a reverse-biased FM-S junction, its nonlinear I-V characteristic, current
saturation, and spin accumulation in S. We show that the spin polarization of
current, spin density, and penetration length increase with the total current
until saturation. We find conditions for most efficient spin injection, which
are opposite to the results of previous works, since the present theory
suggests using a lightly doped resistive semiconductor. It is shown that the
maximal spin polarizations of current and electrons (spin accumulation) can
approach 100% at room temperatures and low current density in a nondegenerate
high-resistance semiconductor. | 0307030v4 |
2003-12-23 | 1-D Simulation of the Electron Density Distribution in a Novel Nonvolatile Resistive Random Access Memory Device | The operation of a novel nonvolatile memory device based on a conductive
ferroelectric/non-ferroelectric thin film multilayer stack is simulated
numerically. The simulation involves the self-consistent steady state solution
of Poisson's equation and the transport equation for electrons assuming a
Drift-Diffusion transport mechanism. Special emphasis is put on the screening
of the spontaneous polarization by conduction electrons as a function of the
applied voltage. Depending on the orientation of the polarization in the
ferroelectric layer, a high and a low resistive state are found giving rise to
a hysteretic I-V characteristic. The R_high to R_low ratio ranging from > 50%
to several orders of magnitude is calculated as a function of the dopant
content. | 0312609v1 |
2004-03-08 | Hole mobility in organic single crystals measured by a "flip-crystal" field-effect technique | We report on single crystal high mobility organic field-effect transistors
(OFETs) prepared on prefabricated substrates using a "flip-crystal" approach.
This method minimizes crystal handling and avoids direct processing of the
crystal that may degrade the FET electrical characteristics. A chemical
treatment process for the substrate ensures a reproducible device quality. With
limited purification of the starting materials, hole mobilities of 10.7, 1.3,
and 1.4 cm^2/Vs have been measured on rubrene, tetracene, and pentacene single
crystals, respectively. Four-terminal measurements allow for the extraction of
the "intrinsic" transistor channel resistance and the parasitic series contact
resistances. The technique employed in this study shows potential as a general
method for studying charge transport in field-accumulated carrier channels near
the surface of organic single crystals. | 0403210v1 |
2004-04-11 | Synthesis of as-grown superconducting MgB_2 thin films by molecular beam epitaxy in UHV conditions | As-grown superconducting MgB_2 thin films have been grown on SrTiO_3(001),
MgO(001), and Al_2O_3(0001) substrates by a molecular beam epitaxy (MBE) method
with novel co-evaporation conditions of low deposition rate in ultra-high
vacuum. The structural and physical properties of the films were studied by
RHEED, XRD, electrical resistivity measurements, and SQUID magnetometer. The
RHEED patterns indicate three-dimensional growth for MgB_2. The highest T_c
determined by resistivity measurement was about 36K in these samples. And a
clear Meissner effect below T_c was observed using magnetic susceptibility
measurement. We will discuss the influence of B buffer layer on the structural
and physical properties. | 0404252v1 |
2004-08-20 | Anomalous Hall effect in insulating Ga1-xMnxAs | We have investigated the effect of doping by Te on the anomalous Hall effect
in Ga1-xMnxAs (x = 0.085). For this relatively high value of x the temperature
dependence of resistivity shows an insulating behavior. It is well known that
in Ga1-xMnxAs the Mn ions naturally act as acceptors. Additional doping by Te
donors decreases the Curie temperature and increases the anomalous Hall
resistivity. With increasing Te concentration the long-range ferromagnetic
order in Ga1-xMnxAs eventually disappears, and paramagnetic-to-spin glass
transition is observed instead. The critical concentration of holes required
for establishing ferromagnetic order in Ga1-xMnxAs (x = 0.085) has been
estimated by using the magnetic polaron percolation theory proposed by Kaminski
and Das Sarma [Phys.Rev.Lett. 88, 247202 (2002)]. | 0408446v1 |
2005-01-14 | Magnetization and magnetoresistance in insulating phases of SrFeO3-d | We report the synthesis and properties of two new insulating phases of
SrFeO3-d with introduction of oxygen deficiencies in metallic SrFeO3 ; one with
0.15 < d < 0.19 (sample A)and the other above d = 0.19 (sample B). Sample A
shows large negative magnetoresistance around the charged ordering (CO)
temperature with magnetic anomalies seen in the temperature dependent
resistivity,magnetization and M-H hysteresis loops. Sample B shows a smooth
insulating behavior with no thermal hysteresis in the resistivity and with a
small positive magnetoresistance. cac and cdc show multiple features associated
with a frustrated magnetic order (helical) due to competing ferro- and
antiferromagnetic interactions. The competing effects of ferro- and
antiferromagnetic phases extend up to T ~ 230 K revealing a new high
temperature scale in this system. These observations are discussed in the
context of magnetic interactions associated with the varying Fe4+/Fe3+ ratio. | 0501352v1 |
2005-07-14 | Field-Dependent Hall Effect in Single Crystal Heavy Fermion YbAgGe below 1K | We report the results of a low temperature (T >= 50 mK) and high field (H <=
180 kOe) study of the Hall resistivity in single crystals of YbAgGe, a heavy
fermion compound that demonstrates field-induced non-Fermi-liquid behavior near
its field-induced quantum critical point. Distinct features in the anisotropic,
field-dependent Hall resistivity sharpen on cooling down and at the base
temperature are close to the respective critical fields for the field-induced
quantum critical point. The field range of the non-Fermi-liquid region
decreases on cooling but remains finite at the base temperature with no
indication of its conversion to a point for T -> 0. At the base temperature,
the functional form of the field-dependent Hall coefficient is field direction
dependent and complex beyond existing simple models thus reflecting the
multi-component Fermi surface of the material and its non-trivial modification
at the quantum critical point. | 0507338v1 |
2005-10-20 | Stick slip motion in grain grain friction in a humid atmosphere | We set up an original apparatus to measure the grain grain friction stress
inside a granular medium composed of sodo-silicate-glass beads surrounded by a
water vapor atmosphere.We analyze here the influence of the physico chemistry
of water on our glass beads and its consequences on our shear experiment. We
found two scales in the analysis of the shear stress signal. On the microscopic
scale of one bead, the experimental results show a dependence on the size of
beads, on the shear rate and on humidity for the resulting stick slip signal.
On the macroscopic scale of the whole assembly of beads, the behavior of the
total amplitude of the shear stress depends on the size of the beads and is
humidity dependent only for relative humidity larger than 80%. For high degrees
of humidity, on the microscopic scale, water lubricates the surface of the
beads leading to a decrease in the microscopic resistance to shear while on the
macroscopic scale the resistance to shear is increased: the assembly of very
humid grains behaves as a non Newtonian fluid. | 0510532v1 |
2006-06-23 | Electronic transport in Si nanowires: Role of bulk and surface disorder | We calculate the resistance and mean free path in long metallic and
semiconducting silicon nanowires (SiNWs) using two different numerical
approaches: A real space Kubo method and a recursive Green's function method.
We compare the two approaches and find that they are complementary: depending
on the situation a preferable method can be identified. Several numerical
results are presented to illustrate the relative merits of the two methods. Our
calculations of relaxed atomic structures and their conductance properties are
based on density functional theory without introducing adjustable parameters.
Two specific models of disorder are considered: Un-passivated, surface
reconstructed SiNWs are perturbed by random on-site (Anderson) disorder whereas
defects in hydrogen passivated wires are introduced by randomly removed H
atoms. The un-passivated wires are very sensitive to disorder in the surface
whereas bulk disorder has almost no influence. For the passivated wires, the
scattering by the hydrogen vacancies is strongly energy dependent and for
relatively long SiNWs (L>200 nm) the resistance changes from the Ohmic to the
localization regime within a 0.1 eV shift of the Fermi energy. This high
sensitivity might be used for sensor applications. | 0606600v1 |
2006-07-18 | Dielectric breakdown in underoxidized magnetic tunnel junctions: Dependence on oxidation time and area | Magnetic tunnel junctions (MTJs) with partially oxidized 9 \AA
AlO$_x$-barriers were recently shown to have the necessary characteristics to
be used as magnetoresistive sensors in high-density storage devices. Here we
study dielectric breakdown in such underoxidized magnetic tunnel junctions,
focusing on its dependence on tunnel junction area and oxidation time. A clear
relation between breakdown mechanism and junction area is observed for the MTJs
with the highest studied oxidation time: samples with large areas fail usually
due to extrinsic causes (characterized by a smooth resistance decrease at
dielectric breakdown). Small area junctions fail mainly through an intrinsic
mechanism (sharp resistance decrease at breakdown). However, this dependence
changes for lower oxidation times, with extrinsic breakdown becoming dominant.
In fact, in the extremely underoxidized magnetic tunnel junctions, failure is
exclusively related with extrinsic causes, independently of MTJ-area. These
results are related with the presence of defects in the barrier (weak spots
that lead to intrinsic breakdown) and of metallic unoxidized Al
nanoconstrictions (leading to extrinsic breakdown). | 0607452v1 |
2007-01-20 | Fabrication and Low Temperature Thermoelectric Properties of Na_xCoO_2 (x = 0.68 and 0.75) Epitaxial Films by the Reactive Solid-Phase Epitaxy | We have fabricated Na_xCoO_2 thin films via lateral diffusion of sodium into
Co_3O_4 (111) epitaxial films (reactive solid-phase epitaxy: Ref. 4). The
environment of thermal diffusion is key to the control of the sodium content in
thin films. From the results of x-ray diffraction and in-plane resistivity, the
epitaxial growth and the sodium contents of these films were identified. The
thermoelectric measurements show a large thermoelectric power similar to that
observed in single crystals. The quasiparticle scattering rate is found to
approach zero at low temperatures, consistent with the small residual
resistivity, indicating high quality of the Na_xCoO_2 thin films. | 0701492v1 |
2007-02-05 | Existence of two electronic states in Sr4Ru3O10 at low temperatures | We report measurements on in-plane resistivity, thermopower, and
magnetization as a function of temperature and magnetic fields on single
crystalline Sr4Ru3O10 grown by the floating zone method. As the temperature was
lowered to below around 30 K, the in-plane and c-axis resistivities and the
thermopower were found to exhibit a step feature accompanied by hysteresis
behavior when the in-plane field was swept up and down from below 10 kOe to
above 20 kOe. The sharp increase in the thermopower with increasing in-plane
magnetic field at low temperatures has not been observed previously in layered
transition metal oxides. Comparing with magnetization data, we propose that the
step feature marks the transition between the two different electronic states
in Sr4Ru3O10. We propose that the alignment of domains by the in-plane magnetic
field is responsible to the emergence of the new electronic states in high
applied in-plane magnetic field. | 0702093v1 |
2007-05-02 | Comment on ``Collapse of Coherent Quasiparticle States in $θ$-(BEDT-TTF)$_2$I$_3$ Observed by Optical Spectroscopy'' | Recently, Takenaka et al. reported that the resistivity rho(T) of
theta-(BEDT-TTF)_2I_3 (theta-ET) exceeds the Ioffe-Regel resistivity by a
factor of 50 at large temperatures T (``bad metal''). This was ascribed to
strong correlation. We argue that the optical conductivity sigma(omega) implies
that correlation is not very strong, and that correlation gives no general
strong suppression of sigma(omega). The large rho(T) is primarily due to a
downturn in sigma(omega) at small omega, earlier emphasized by Takenaka et al.
as the explanation for bad metal behavior of high-T_c cuprates. We argue,
however, that for cuprates strong correlation is the main effect. The data of
Takenaka et al. puts theta-ET in a new class of bad metals. | 0705.0230v1 |
2007-07-15 | Physical properties of a new cuprate superconductor Pr_2Ba_4Cu_7O_{15-δ} | We present studies of the thermal, magnetic and electrical transport
properties of reduced polycrystalline Pr_2Ba_4Cu_7O_{15-\delta} (Pr247) showing
a superconducting transition at Tc = 10 - 16 K and compare them with those of
as-sintered non-superconducting Pr247. The electrical resistivity in the normal
state exhibited T2 dependence up to approximately 150 K. A clear specific heat
anomaly was observed at Tc for Pr247 reduced in a vacuum for 24 hrs, proving
the bulk nature of the superconducting state. By the reduction treatment, the
magnetic ordering temperature TN of Pr moments decreased from 16 to 11 K, and
the entropy associated with the ordering increased, while the effective
paramagnetic moments obtained from the DC magnetic susceptibility varied from
2.72 to 3.13 mB. The sign of Hall coefficient changed from positive to negative
with decreasing temperature in the normal state of a superconducting Pr247,
while that of as-sintered one was positive down to 5 K. The electrical
resistivity under high magnetic fields was found to exhibit T^a dependence (a =
0.08 - 0.4) at low temperatures. A possibility of superconductivity in the
so-called CuO double chains is discussed. | 0707.2180v1 |
2007-07-30 | Intrinsic tunneling in phase separated manganites | We present evidence of direct electron tunneling across intrinsic insulating
regions in sub-micrometer wide bridges of the phase separated ferromagnet
(La,Pr,Ca)MnO$_3$. Upon cooling below the Curie temperature, a predominantly
ferromagnetic supercooled state persists where tunneling across the intrinsic
tunnel barriers (ITBs) results in metastable, temperature-independent,
high-resistance plateaus over a large range of temperatures. Upon application
of a magnetic field, our data reveal that the ITBs are extinguished resulting
in sharp, colossal, low-field resistance drops. Our results compare well to
theoretical predictions of magnetic domain walls coinciding with the intrinsic
insulating phase. | 0707.4411v2 |
2008-01-09 | Impact of in-plane currents on magnetoresistance properties of an exchange-biased spin-valve with insulating antiferromagnetic layer | The impact of in-plane alternating currents on the exchange bias, resistance,
and magnetoresistance of a CoFe/NiCoO/CoFe/Cu/CoFe spin-valve is studied. With
increasing current, the resistance is increased while the maximum
magnetoresistance ratio decreases. Noticeably, the reversal of the pinned layer
is systematically suppressed in both field sweeping directions. Since the NiCoO
oxide is a good insulator, it is expected that the ac current flows only in the
CoFe/Cu/CoFe top layers, thus ruling out any presence of spin-transfer torque
acting on the spins in the antiferromagnetic layer. Instead, our measurements
show clear evidences for the influence of Joule heating caused by the current.
Moreover, results from temperature-dependent measurements very much resemble
those of the current dependence, indicating that the effect of Joule heating
plays a major role in the current-in-plane spin-valve configurations. The
results also suggest that spin-transfer torques between ferromagnetic layers
might still exist and compete with the exchange bias at sufficiently high
currents. | 0801.1515v1 |
2008-04-09 | Curie point singularity in the temperature derivative of resistivity in (Ga,Mn)As | We observe a singularity in the temperature derivative $d\rho/dT$ of
resistivity at the Curie point of high-quality (Ga,Mn)As ferromagnetic
semiconductors with $T_c$'s ranging from approximately 80 to 185 K. The
character of the anomaly is sharply distinct from the critical contribution to
transport in conventional dense-moment magnetic semiconductors and is
reminiscent of the $d\rho/dT$ singularity in transition metal ferromagnets.
Within the critical region accessible in our experiments, the temperature
dependence on the ferromagnetic side can be explained by dominant scattering
from uncorrelated spin fluctuations. The singular behavior of $d\rho/dT$ on the
paramagnetic side points to the important role of short-range correlated spin
fluctuations. | 0804.1578v2 |
2008-06-24 | Low temperature thermal resistance for a new design of silver sinter heat exchanger | We have developed a novel procedure for constructing high surface area silver
sinter heat exchangers. Our recipe incorporates nylon fibers having a diameter
of ~ 50 microns and thin wires of bulk silver in the heat exchanger. In order
to increase the thermal conductance of liquid helium within the heat exchanger,
prior to sintering, the nylon fibers are dissolved with an organic acid leaving
a network of channels. In addition, the silver wires reinforce the structural
integrity, and reduce the resistance, of the silver sinter. We have constructed
a 3-He melting curve thermometer (MCT) with this type of heat exchanger and
measured the thermal time response of the liquid 3-He inside the MCT in the
temperature range T = 2-150 mK. We find a thermal relaxation time of ~ 490 s at
T ~ 1 mK. We have used scanning electron microscopy (SEM) to characterize the
heat exchanger and BET absorption for determination of the specific surface
area. | 0806.3930v1 |
2008-08-09 | Transport and Magnetic properties of Fe1/3VSe2 | Electrical conductivity, thermopower and magnetic properties of
Fe-intercalated Fe0.33VSe2 has been reported between 4.2K - 300K. We observe a
first order transition in the resistivity of the sintered pellets around 160K
on cooling. The electronic properties including the transitional hysteresis in
the resistance anomaly (from 80K-160K) are found to be very sensitive to the
structural details of the samples, which were prepared in different annealing
conditions. The thermopower results on the sintered pellets are reported
between 10K - 300K. The magnetic measurements between 2K - 300K and up to 14
Tesla field show the absence of any magnetic ordering in Fe0.33VSe2. The
magnetic moment per Fe -atom at room temperature (between 1.4 to 1.7 Bohr
Magneton) is much lower than in previously reported anti-ferromagnetic FeV2Se4.
Furthermore, the Curie constant shows a rapid and continuous reduction and
combined with the high field magnetization result at 2K suggests a rapid
decrease in the paramagnetic moments on cooling to low temperatures and the
absence of any magnetic order in Fe0.33VSe2 at low temperatures. | 0808.1334v1 |
2008-08-28 | Giant frictional drag in strongly interacting bilayers near filling factor one | We study the frictional drag in high mobility, strongly interacting GaAs
bilayer hole systems in the vicinity of the filling factor $\nu=1$ quantum Hall
state (QHS), at the same fillings where the bilayer resistivity displays a
reentrant insulating phase. Our measurements reveal a very large longitudinal
drag resistivity ($\rho^{D}_{xx}$) in this regime, exceeding 15 k$\Omega/\Box$
at filling factor $\nu=1.15$. $\rho^{D}_{xx}$ shows a weak temperature
dependence and appears to saturate at a finite, large value at the lowest
temperatures. Our observations are consistent with theoretical models positing
a phase separation, e.g. puddles of $\nu=1$ QHS embedded in a different state,
when the system makes a transition from the coherent $\nu=1$ QHS to the weakly
coupled $\nu=2$ QHS. | 0808.3807v1 |
2008-10-26 | Development of Glass Resistive Plate Chambers for INO | The India-based Neutrino Observatory (INO) collaboration is planning to build
a massive 50kton magnetised Iron Calorimeter (ICAL) detector, to study
atmospheric neutrinos and to make precision measurements of the parameters
related to neutrino oscillations. Glass Resistive Plate Chambers (RPCs) of
about 2m X 2m in size are going to be used as active elements for the ICAL
detector. We have fabricated a large number of glass RPC prototypes of 1m X 1m
in size and have studied their performance and long term stability. In the
process, we have developed and produced a number of materials and components
required for fabrication of RPCs. We have also designed and optimised a number
of fabrication and quality control procedures for assembling the gas gaps. In
this paper we will review our activities towards development of glass RPCs for
the INO ICAL detector and will present results of the characterisation studies
of the RPCs. | 0810.4693v1 |
2009-02-01 | Enhancement of positive magnetoresistance following a magnetic-field-induced ferromagnetic transition in an intermetallic compound, Tb5Si3 | We report the existence of a field-induced ferromagnetic transition in the
magnetically ordered state (<69 K) of an intermetallic compound, Tb5Si3, and
this transition is distinctly first-order at 1.8 K (near 60 kOe), whereas it
appears to become second order near 20 K. The finding we stress is that the
electrical resistivity becomes suddenly large in the high-field state after
this transition and this is observed in the entire temperature range in the
magnetically ordered state. Such an enhancement of 'positive' magnetoresistance
(below 100 kOe) at the metamagnetic transition field is unexpected on the basis
that the application of magnetic field should favor a low-resistive state due
to alignment of spins. | 0902.0153v1 |
2009-06-08 | Tunneling Electroresistance in Ferroelectric Tunnel Junctions with a Composite Barrier | Tunneling electroresistance (TER) effect is the change in the electrical
resistance of a ferroelectric tunnel junction (FTJ) associated with
polarization reversal in the ferroelectric barrier layer. Here we predict that
a FTJ with a composite barrier that combines a functional ferroelectric film
and a thin layer of a non-polar dielectric can exhibit a significantly enhanced
TER. Due to the change in the electrostatic potential with polarization
reversal the non-polar dielectric barrier acts as a switch that changes its
barrier height from a low to high value. The predicted values of TER are giant
and indicate that the resistance of the FTJ can be changed by many orders in
magnitude at the coercive electric field of ferroelectric. | 0906.1524v1 |
2009-08-11 | Contrasting Pressure Effects in Sr2VFeAsO3 and Sr2ScFePO3 | We report the resistivity measurements under pressure of two Fe-based
superconductors with a thick perovskite oxide layer, Sr2VFeAsO3 and Sr2ScFePO3.
The superconducting transition temperature Tc of Sr2VFeAsO3 markedly increases
with increasing pressure. Its onset value, which was Tc{onset}=36.4 K at
ambient pressure, increases to Tc{onset}=46.0 K at ~4 GPa, ensuring the
potential of the "21113" system as a high-Tc material. However, the
superconductivity of Sr2ScFePO3 is strongly suppressed under pressure. The
Tc{onset} of ~16 K decreases to ~5 K at ~4 GPa, and the zero-resistance state
is almost lost. We discuss the factor that induces this contrasting pressure
effect. | 0908.1469v2 |
2010-03-11 | Nonlinear response and two stable electrical conductivity levels measured in plasticized PVC thin film samples | The electrical conductivity of PVC films prepared with a patented plasticizer
of type "A" was measured with high precision automated setup, based on standard
ring sell with a voltage range much less than breakdown voltage. Continual
voltage-current measurements permit to take into account Debay relaxation
process and clearly distinguish specific polymer film conductivity effects,
connected with continuous current-stabilization behavior and transitions
between two stable (long-living) states with several order magnitude different
conductivities. Spontaneous reversible and non-destructive transitions of
resistance levels was observed. For 30 mkm polymer films the values of sample
resistance was measured equal to: high- 106 Ohm and low -103 Ohm. | 1003.2331v1 |
2010-09-13 | Non-monotonic temperature dependent transport in graphene grown by Chemical Vapor Deposition | Temperature-dependent resistivity of graphene grown by chemical vapor
deposition (CVD) is investigated. We observe in low mobility CVD graphene
device a strong insulating behavior at low temperatures and a metallic behavior
at high temperatures manifesting a non-monotonic in the temperature dependent
resistivity.This feature is strongly affected by carrier density modulation. To
understand this anomalous temperature dependence, we introduce thermal
activation of charge carriers in electron-hole puddles induced by randomly
distributed charged impurities. Observed temperature evolution of resistivity
is then understood from the competition among thermal activation of charge
carriers, temperature-dependent screening and phonon scattering effects. Our
results imply that the transport property of transferred CVD-grown graphene is
strongly influenced by the details of the environment | 1009.2506v2 |
2010-10-14 | Viscous corrections to the resistance of nano-junctions: a dispersion relation approach | It is well known that the viscosity of a homogeneous electron liquid diverges
in the limits of zero frequency and zero temperature. A nanojunction breaks
translational invariance and necessarily cuts off this divergence. However, the
estimate of the ensuing viscosity is far from trivial. Here, we propose an
approach based on a Kramers-Kr\"onig dispersion relation, which connects the
zero-frequency viscosity, $\eta(0)$, to the high-frequency shear modulus,
$\mu_{\infty}$, of the electron liquid via $\eta(0) =\mu_{\infty} \tau$, with
$\tau$ the junction-specific momentum relaxation time. By making use of a
simple formula derived from time-dependent current-density functional theory we
then estimate the many-body contributions to the resistance for an integrable
junction potential and find that these viscous effects may be much larger than
previously suggested for junctions of low conductance. | 1010.2959v2 |
2011-05-18 | Multiple photoexcitation of two-dimensional electron systems: bichromatic magnetoresistance oscillations revisited | We analyze theoretically magnetoresistance of high mobility two-dimensional
electron systems being illuminated by multiple radiation sources. In
particular, we study the influence on the striking effect of microwave-induced
resistance oscillations. We consider moderate radiation intensities without
reaching the zero resistance states regime. We use the model of
radiation-driven Larmor orbits extended to several light sources. First, we
study the case of two different radiations polarized in the same direction with
different or equal frequencies. For both cases we find a regime of
superposition or interference of harmonic motions. When the frequencies are
different, we obtain a modulated magnetoresistance response with pulses and
beats. On the other hand, when the frequencies are the same, we find that the
final result will depend on the phase difference between both radiation fields
going from an enhanced response to a total collapse of oscillations, reaching
an outcome similar to darkness. Finally, we consider a multiple photoexcitation
case (three different frquencies) where we propose the two-dimensional electron
system as a potential nanoantenna device for microwaves. | 1105.3592v1 |
2011-07-11 | Impairment of double exchange mechanism in electron transport of iron pnictides | Double exchange mechanism is believed to favor transport along ferromagnetic
directions, the failure of which in explaining the unusual resistivity
anisotropy in iron pnictides is investigated. Several factors intrinsic to the
microscopic mechanism of transport in iron pnictides are identified and
analyzed, including the moderate Hund's coupling, low local moment, and
presence of two anisotropic degenerate orbitals xz and yz. In particular, the
substantial second neighbor hoppings are found to be decisive in giving results
opposite to the double exchange picture. In high temperature nonmagnetic phase,
orbital ordering is shown to give the right trend of resistivity anisotropy as
observed experimentally, advocating its essential role in electron transport of
iron pnictides. | 1107.1952v1 |
2011-10-24 | Anisotropy of upper critical fields and thermally-activated flux flow of quenched KxFe2-ySe2 single crystals | We report the anisotropy of the upper critical fields mu0Hc2(T) and
thermally-activated flux flow (TAFF) behavior of quenched KxFe2-ySe2. Even
though the post-annealing and quenching process enhances the superconducting
volume fraction, it has a minor effect on the upper critical fields for H//c
and H//ab. Analysis of the angular-dependence of resistivity rho_ab(theta,H)
indicates that it follows the scaling law based on the anisotropic
Ginzburg-Landau (GL) theory and the anisotropy Gamma(T) increases with
decreasing temperature with Gamma(T) ~ 3.6 at 27 K. The resistivity of quenched
sample exhibits an Arrhenius TAFF behavior for both field directions. Field
dependence of thermally activated energy U0(H) implies that the collective flux
creep is dominant in high fields and point defects are the main pinning source
in this regime. | 1110.5316v1 |
2011-10-26 | Mg substitution in CuCrO2 delafossite compounds | A detailed investigation of the series CuCr(1-x)MgxO2 (x = 0.0 - 0.05) has
been performed by making high-temperature resistivity and thermopower
measurements, and by performing a theoretical analysis of the latter.
Microstructure characterization has been carried out as well. Upon Mg2+ for
Cr3+ substitution, a concomitant decrease in the electrical resistivity and
thermopower values is found, up to x ~ 0.02 - 0.03, indicating a low solubility
limit of Mg in the structure. This result is corroborated by scanning electron
microscopy observations, showing the presence of MgCr2O4 spinels as soon as x =
0.005. The thermopower is discussed in the temperature-independent correlation
functions ratio approximation as based on the Kubo formalism, and the
dependence of the effective charge carrier density on the nominal Mg
substitution rate is addressed. This leads to a solubility limit of 1.1% Mg in
the delafossite, confirmed by energy dispersive X-ray spectroscopy analysis. | 1110.5730v2 |
2011-11-09 | Insulator-to-metal transition and large thermoelectric effect in La$_{1-x}$Sr$_{x}$MnAsO | We report the Sr substitution effect in an antiferromagnetic insulator
LaMnAsO. The Sr doping limit is $x\sim$ 0.10 under the synthesis conditions, as
revealed by x-ray diffractions indicate. Upon Sr doping, the room-temperature
resistivity drops by five orders of magnitude down to $\sim$0.01
$\Omega\cdot$cm, and the temperature dependence of resistivity shows
essentially metallic behavior for $x\geq$0.08. Hall and Seebeck measurements
confirm consistently that the insulator-to-metal transition is due to hole
doping. Strikingly, the room-temperature Seebeck coefficient for the metallic
samples is as high as $\sim240 \mu$V/K, making the system as a possible
candidate for thermoelectric applications. | 1111.2232v1 |
2011-11-23 | Magneto-Electric Effects on Sr Z-type Hexaferrite at Room Temperature | In this paper, magnetoelectric effects of Sr Z-type hexaferrite,
Sr3Fe24Co2O41, at room temperature is measured. The change in remanence
magnetization was measured by applying a DC voltage or electric field across a
slab of hexaferrite. Changes of ~ 18% in remanence was observed in an electric
field of 10,000V/cm implying a similar change in the microwave permeability at
frequencies below 3GHz. Also, a change in dielectric constant at 1 GHz of ~16%
in a magnetic field of only 320 Oe was measured. In these types of measurements
high resistivity is critical in order to reduce current flow in the
hexaferrite. The resistivity of the hexaferrite was raised to 4.28x10^8 ohm-cm
by annealing under oxygen pressure. The measurements indicate that indeed
electric polarization and magnetization changes were induced by the application
of magnetic and electric fields, respectively. The implications for microwave
applications appear to be very promising at room temperature. | 1111.5555v1 |
2011-11-23 | Room Temperature Magnetoelectric Effects on Single Slabs of Z-type Hexaferrites | In this paper, magnetoelectric effects of Sr Z-type hexaferrite,
Sr3Fe24Co2O41, at room temperature is measured. The change in remanence
magnetization was measured by applying a DC voltage or electric field across a
slab of hexaferrite. Changes of ~ 18% in remanence was observed in an electric
field of 10,000V/cm implying a similar change in the microwave permeability at
frequencies below 3GHz. In these types of measurements high resistivity is
critical in order to reduce current flow in the hexaferrite. The resistivity of
the hexaferrite was raised to 4.28x10^8 ohm?-cm by annealing under oxygen
pressure. The measurements indicate that indeed electric polarization and
magnetization changes were induced by the application of magnetic and electric
fields, respectively. The implications for microwave applications appear to be
very promising at room temperature. | 1111.5556v1 |
2012-02-05 | Temperature dependent elastic constants and ultimate strength of graphene and graphyne | Based on the first principles calculation combined with quasi-harmonic
approximation, in this work we focus on the analysis of temperature dependent
lattice geometries, thermal expansion coefficients, elastic constants and
ultimate strength of graphene and graphyne. For the linear thermal expansion
coefficient, both graphene and graphyne show a negative region in the low
temperature regime. This coefficient increases up to be positive at high
temperatures. Graphene has superior mechanical properties, with Young modulus
E11=371.0 N/m, E22=378.2 N/m and ultimate tensile strength of 119.2 GPa at room
temperature. Based on our analysis, it is found that graphene's mechanical
properties have strong resistance against temperature increase up to 1200 K.
Graphyne also shows good mechanical properties, with Young modulus E11=224.7
N/m, E22=223.9 N/m and ultimate tensile strength of 81.2 GPa at room
temperature, but graphyne's mechanical properties have a weaker resistance with
respect to the increase of temperature than that of graphene. | 1202.0933v1 |
2012-02-08 | Coexisting Holes and Electrons in High-Tc Materials: Implications from Normal State Transport | Normal state resistivity and Hall effect are shown to be successfully modeled
by a two-band model of holes and electrons that is applied self-consistently to
(i) DC transport data reported for eight bulk-crystal and six oriented-film
specimens of YBa2Cu3O7-{\delta}, and (ii) far-infrared Hall angle data reported
for YBa2Cu3O7-{\delta} and Bi2Sr2CaCu2O8+{\delta}. The electron band exhibits
extremely strong scattering; the extrapolated DC residual resistivity of the
electronic component is shown to be consistent with the previously observed
excess thermal conductivity and excess electrodynamic conductivity at low
temperature. Two-band hole-electron analysis of Hall angle data suggest that
the electrons possess the greater effective mass. | 1202.1792v1 |
2012-07-25 | Superconductivity at 5.4 K in $β$-Bi$_2$Pd | We investigate bulk superconductivity in a high-quality single crystal of
Bi$_2$Pd ($\beta$-Bi$_2$Pd, space group; I4/mmm) at temperatures less than 5.4
K by exploring its electrical resistivity, magnetic susceptibility, and
specific heat. The temperature dependence of the electrical resistivity shows
convex-upward behaviors at temperatures greater than 40-50 K, which can be
explained by a parallel-resistor model. In addition, we demonstrate that this
material is a multiple-band/multiple-gap superconductor based on the
temperature dependences of the specific heat and the upper critical field. | 1207.5905v3 |
2012-10-09 | Giant exchange bias and ferromagnetism in the CoO shell of Co/CoO-MgO core-shell nanoparticles | Using magnetron sputtering, we produced a series of Co/CoO-MgO nanoparticles
on Si(100) substrates. High-resolution transmission electron microscopy (HRTEM)
image shows that small isolated Co-clusters (core) covered with CoO (shells)
with a size of a few nm embedded in a MgO matrix. Resistivity as a function of
Co atomic ratio exhibits a distinct percolation threshold with a sharp decrease
around 69% Co content. Across the threshold, the resistivity drops about 7
orders of magnitude. For a sample at this percolation critical threshold, we
have observed a giant exchange bias field HE=2460 Oe at T= 2K, and using soft
x-ray magnetic circular dichroism at the Co-L2,3 edge, we have detected a
ferromagnetic (FM) signal originating from the antiferromagnetic CoO shell.
Moreover, decreasing the Mg-impurities will reduce the FM signal from CoO shell
(namely the uncompensated spin density) and the size of HE, thus directly
support the uncompensated spin model. | 1210.2510v1 |
2012-11-12 | Density dependent electrical conductivity in suspended graphene: Approaching the Dirac point in transport | We theoretically consider, comparing with the existing experimental
literature, the electrical conductivity of gated monolayer graphene as a
function of carrier density, temperature, and disorder in order to assess the
prospects of accessing the Dirac point using transport studies in high-quality
suspended graphene. We show that the temperature dependence of graphene
conductivity around the charge neutrality point provides information about how
close the system can approach the Dirac point although competition between
long-range and short-range disorder as well as between diffusive and ballistic
transport may considerably complicate the picture. We also find that acoustic
phonon scattering contribution to the graphene resistivity is always relevant
at the Dirac point in contrast to higher density situations where the acoustic
phonon contribution to the resistivity is strongly suppressed at the low
temperature Bloch-Gr\"{u}neisen regime. We provide detailed numerical results
for temperature and density dependent conductivity for suspended graphene. | 1211.2845v2 |
2012-12-26 | Molybdenum sputtering film characterization for high gradient accelerating structures | Technological advancements are strongly required to fulfill the demands of
new accelerator devices with the highest accelerating gradients and operation
reliability for the future colliders. To this purpose an extensive R&D
regarding molybdenum coatings on copper is in progress. In this contribution we
describe chemical composition, deposition quality and resistivity properties of
different molybdenum coatings obtained via sputtering. The deposited films are
thick metallic disorder layers with different resistivity values above and
below the molibdenum dioxide reference value. Chemical and electrical
properties of these sputtered coatings have been characterized by Rutherford
backscattering, XANES and photoemission spectroscopy. We will also present a
three cells standing wave section coated by a molybdenum layer $\sim$ 500 nm
thick designed to improve the performance of X-Band accelerating systems. | 1212.6203v1 |
2012-12-28 | Magneto-resistance up to 60 Tesla in Topological Insulator Bi2Te3 Thin Films | We report magneto-transport studies of topological insulator Bi_{2}Te_{3}
thin films grown by pulsed laser deposition. A non-saturating linear-like
magneto-resistance (MR) is observed at low temperatures in the magnetic field
range from a few Tesla up to 60 Tesla. We demonstrate that the strong
linear-like MR at high field can be well understood as the weak
antilocalization phenomena described by Hikami-Larkin-Nagaoka theory. Our
analysis suggests that in our system, a topological insulator, the elastic
scattering time can be longer than the spin-orbit scattering time. We briefly
discuss our results in the context of Dirac Fermion physics and 'quantum linear
magnetoresistance'. | 1212.6464v1 |
2013-01-02 | Visualizing Atomic-Scale Negative Differential Resistance in Bilayer Graphene | We investigate the atomic-scale tunneling characteristics of bilayer graphene
on silicon carbide using the scanning tunneling microscopy. The high-resolution
tunneling spectroscopy reveals an unexpected negative differential resistance
(NDR) at the Dirac energy, which spatially varies within the single unit cell
of bilayer graphene. The origin of NDR is explained by two near-gap van Hove
singularities emerging in the electronic spectrum of bilayer graphene under a
transverse electric field, which are strongly localized on two sublattices in
different layers. Furthermore, defects near the tunneling contact are found to
strongly impact on NDR through the electron interference. Our result provides
an atomic-level understanding of quantum tunneling in bilayer graphene, and
constitutes a useful step towards graphene-based tunneling devices. | 1301.0270v1 |
2013-04-01 | Pressure Induced Superconductivity and Structural Transitions in Ba(Fe0.9Ru0.1)2As2 | High pressure electrical resistance and x-ray diffraction measurements have
been performed on ruthenium-doped Ba(Fe0.9Ru0.1)2As2, up to pressures of 32 GPa
and down to temperatures of 10 K, using designer diamond anvils under
quasi-hydrostatic conditions. At 3.9 GPa, there is an evidence of
pressure-induced superconductivity with Tc onset of 24 K and zero resistance at
Tc zero of ~14.5 K. The superconducting transition temperature reaches maximum
at ~5.5 GPa and then decreases gradually with increase in pressure before
completely disappearing above 11.5 GPa. Upon increasing pressure at 200 K, an
isostructural phase transition from a tetragonal (I4/mmm) phase to a collapsed
tetragonal phase is observed at 14 GPa and the collapsed phase persists up to
at least 30 GPa. The changes in the unit cell dimensions are highly anisotropic
across the phase transition and are qualitatively similar to those observed in
undoped BaFe2As2 parent. | 1304.0298v2 |
2013-04-10 | Charge Kondo Effect in Thermoelectric Properties of Lead Telluride doped with Thallium Impurities | We investigate the thermoelectric properties of PbTe doped with a small
concentration $x$ of Tl impurities acting as acceptors and described by
Anderson impurities with negative on-site (effective) interaction. The
resulting charge Kondo effect naturally accounts for a number of the low
temperature anomalies in this system, including the unusual doping dependence
of the carrier concentration, the Fermi level pinning and the self-compensation
effect. The Kondo anomalies in the low temperature resistivity at temperatures
$T\leq 10\, {\rm K}$ and the $x$-dependence of the residual resistivity are
also in good agreement with experiment. Our model also captures the qualitative
aspects of the thermopower at higher temperatures $T>300\, {\rm K}$ for high
dopings ($x>0.6%$) where transport is expected to be largely dominated by
carriers in the heavy hole band of PbTe. | 1304.3026v1 |
2013-04-22 | Modeling Composites of Multi-Walled Carbon Nanotubes in Polycarbonate | High strain rate experiments performed on multi-walled carbon nanotubes and
polycarbonate composites (MWCNT-PC) have exhibited enhanced impact resistance
under a dynamic strain rate of nearly 2500/s with composition of only 0.5 to
2.0 percent of Multi walled carbon nanotubes(MWCNTs) in pure polycarbonate(PC).
Similarly, hardness and elastic modulus under static loads resulted in
significant increase depending upon the composition of MWCNTs in PC.The present
work aims to analyze these results by correlating the data to fit expressions
in generalizing the behavior of MWCNTs composition for MWCNT-PC composites
under both static and impact loads. As a result we found that an optimum
composition of 2.1 percent of MWCNTs exhibits maximum stress resistance within
elastic range under strain rates of nearly 2500/s for MWCNT-PC composites.The
results are critically dependent on the composition of MWCNTs and significantly
deteriorate below and above a threshold composition. A simple model based on
Lennard-Jones atom-atom based potential is formulated to compute static
properties of pure as well as composites of PC. | 1304.5979v1 |
2013-08-15 | Suppression of bulk conductivity in InAs/GaSb broken gap composite quantum wells | The two-dimensional topological insulator state in InAs/GaSb quantum wells
manifests itself by topologically protected helical edge channel transport
relying on an insulating bulk. This work investigates a way of suppressing bulk
conductivity by using gallium source materials of different degrees of impurity
concentrations. While highest-purity gallium is accompanied by clear conduction
through the sample bulk, intentional impurity incorporation lead to a bulk
resistance over 1 M\Omega. This resistance was found to be independent of
applied magnetic fields. Ultra high electron mobilities for GaAs/AlGaAs
structures fabricated in a molecular beam epitaxy system used for the growth of
Sb-based samples are reported. | 1308.3375v2 |
2013-09-06 | Heteroepitaxy of Group IV-VI Nitrides by Atomic Layer Deposition | Heteroepitaxial growth of selected group IV-VI nitrides on various
orientations of sapphire (\alpha-Al2O3) is demonstrated using atomic layer
deposition. High quality, epitaxial films are produced at significantly lower
temperatures than required by conventional deposition methods. Characterization
of electrical and superconducting properties of epitaxial films reveals a
reduced room temperature resistivity and increased residual resistance ratio
(RRR) for films deposited on sapphire compared to polycrystalline samples
deposited concurrently on fused quartz substrates. | 1309.1789v1 |
2013-10-31 | Single crystal growth and characterization of the large-unit-cell compound Cu13Ba | Single crystals of Cu$_{13}$Ba were successfully grown out of Ba-Cu self
flux. Temperature dependent magnetization, $M(T)$, electrical resistivity,
$\rho(T)$, and specific heat, $C_p(T)$, data are reported. Isothermal
magnetization measurements, $M(H)$, show clear de Haas-van Alphen oscillations
at $T$ = 2 K for applied fields as low as $\mu_0H$ = 1T. An anomalous behavior
of the magnetic susceptibility is observed up to $T$ ~ 50K reflecting the
effect of de Haas-van Alphen oscillations at fairly high temperatures. The
field- and temperature-dependencies of the magnetization indicate the presence
of diluted magnetic impurities with a concentration of the order of 0.01at.%.
Accordingly, the minimum and lower temperature rise observed in the electrical
resistivity at and below $T$ = 15K is attributed to the Kondo impurity effect. | 1311.0027v1 |
2013-11-22 | Thermally excited multi-band conduction in LaAlO3/SrTiO3 heterostructures exhibiting magnetic scattering | Magnetotransport measurements of charge carriers at the interface of a
LaAlO3/SrTiO3 heterostructure with 26 unit cells of LaAlO3 show Hall resistance
and magnetoresistance which at low and high temperatures is described by a
single channel of electron-like charge carriers. At intermediate temperatures,
we observe non-linear Hall resistance and positive magnetoresistance,
establishing the presence of at least two electron-like channels with
significantly different mobilities and carrier concentrations. These channels
are separated by 6 meV in energy and their temperature dependent occupation and
mobilities are responsible for the observed transport properties of the
interface. We observe that one of the channels has a mobility that decreases
with decreasing temperature, consistent with magnetic scattering in this
channel. | 1311.5807v1 |
2014-04-18 | Systematic control of carrier concentration and resisitivity in RF sputtered Zinc oxide thin films | RF sputtered ZnO and Al:ZnO films are attractive transparent conductive
oxides for fabrication of opto-electronic devices. In this paper we present
efforts to control carrier concentration and mobility of ZnO/Al:ZnO thin films
by controlling deposition parameters (RF power, pressure and substrate
temperature. Al:ZnO thin film with resistivity as low as $\rho$ = $3.8\times
10^{-4}$ $\Omega$.cm at deposition temperature of 250{\deg}C has been achieved.
Zinc oxide thin film with low resistivity of $\rho$ = $3.7\times 10^{-2}$
$\Omega$.cm and high electron mobility of $30$ $\mathrm{cm^{-2}V^{-1}s^{-1}}$
at deposition temperature of 250{\deg}C with acceptable electronic parameters
stability has been obtained.Light transmission of Al:ZnO and ZnO samples
deposited on glass at different substrate temperature has been studied.
Investigation were made to assess the effect of deposition temperature on the
photoluminescence spectra (PL) of ZnO/Al:ZnO sputtered on silicon and glass
substrate. The evolution of near band edge (NBE) and deep level emission (DLE)
photoluminescence peaks with deposition temperature in ZnO/Al:ZnO sputtered on
Silicon and glass substrate have been studied. | 1404.4902v1 |
2014-04-17 | Caracterización de austenita expandida generada por cementación iónica de aceros inoxidables. Estudio de la estabilidad frente a la irradiación con haces de iones ligeros energéticos | This thesis was focused on the surface modification with plasma discharge.
Austenitic AISI 316L stainless steel sample was carburised under different
experimental conditions and mechanical properties have been studied (thickness,
lattice parameter, elemental composition, hardness, wear resistance and
corrosion resistance). After that, steel substrates have been nitrided or
carburised in order to analyse their stability under ion bombardment using a
plasma focus device. Helium and deuterium were the gases used in 0, 1, 5, and
10 discharges. Optical and X-ray characterisations were used. Finally, using
magnetron sputtering nitrided/carburised samples were coated with an AlN thin
film in order to study their stability under long treatments at high
temperatures. | 1404.5204v1 |
2014-05-05 | Controllable growth of Al nanorods for inexpensive and degradation-resistant surface enhanced Raman spectroscopy | Surface enhanced Raman spectroscopy (SERS) has the capacity of detecting
trace amount of biological or chemical matter, even single molecules, through
the use of metallic nanostructures such as nanorods. Silver (Ag) and gold (Au)
nanorods have led to the impressive enhancement of Raman signals, but they are
either expensive, degrade fast over time, or suffer from poor sample
repeatability. In contrast, Al is much less expensive, and Al nanorods could
potentially be resistant to degradation over time due to the protection from
native aluminum-oxide layers. Unfortunately, the controllable growth of Al
nanorods has not been reported so far. This Letter reports, for the first time,
the controllable growth of Al nanorods using physical vapor deposition (PVD);
through the use of oxygen (O) surfactants. The enhancement factor of the Al
nanorods in SERS is as high as 1250, and shows nearly no degradation after
storage in ambient for 30 days or annealing at 475 K for one day. | 1405.1009v1 |
2014-06-27 | Simulation of Non-linear SRF losses derived from characteristic topography of etched and electropolished niobium surfaces | A simplified numerical model has been developed to simulate non-linear
superconducting radiofrequency (SRF) losses on Nb surfaces. This study focuses
exclusively on excessive surface resistance (Rs) losses due to the microscopic
topographical magnetic field enhancements. When the enhanced local surface
magnetic field exceeds the superconducting critical transition magnetic field
Hc, small volumes of surface material may become normal conducting and increase
the effective surface resistance without inducing a quench. Using topographic
data from typical Buffered Chemical Polish (BCP) and Electropolish (EP) treated
fine grain niobium , we have estimated the resulting field-dependent losses and
extrapolated this model to the implications for cavity performance. The model
predictions correspond well to the characteristic BCP versus EP high field Q0
performance differences for fine grain niobium. We describe the algorithm of
the model, its limitations, and the effects of this non-linear loss
contribution on SRF cavity performance. | 1406.7276v4 |
2015-01-25 | Superconductivity in Dense Rashba Semiconductor BiTeCl | Layered non-centrosymmetric bismuth tellurohalides are being examined as
candidates for topological insulators. Pressure is believed to be essential for
inducing and tuning topological order in these systems. Through electrical
transport and Raman scattering measurements, we find superconductivity in two
high-pressure phases of BiTeCl with the different normal state features,
carrier characteristics, and upper critical field behaviors. Superconductivity
emerges when the resistivity maximum or charge density wave is suppressed by
the applied pressure and then persists till the highest pressure of 51 GPa
measured. The huge enhancement of the resistivity with three magnitude of
orders indicates the possible achievement of the topological order in the dense
insulating phase. These findings not only enrich the superconducting family
from topological insulators but also pave the road on the search of topological
superconductivity in bismuth tellurohalides. | 1501.06203v1 |
2015-02-04 | Topological Insulator Thin Films Starting from the Amorphous Phase - Bi$_2$Se$_3$ as Example | We present a new method to obtain topological insulator Bi$_2$Se$_3$ thin
films with a centimeter large lateral length. To produce amorphous Bi$_2$Se$_3$
thin films we have used a sequential flash-evaporation method at room
temperature. Transmission electron microscopy has been used to verify that the
prepared samples are in a pure amorphous state. During annealing the samples
transform into the rhombohedral Bi$_2$Se$_3$ crystalline strcuture which was
confirmed using X-ray diffraction and Raman spectroscopy. Resistance
measurements of the amorphous films show the expected Mott variable range
hopping conduction process with a high specific resistance compared to the one
obtained in the crystalline phase (metallic behavior). We have measured the
magnetoresistance (MR) and the Hall effect (HE) at different temperatures
between 2 K and 275 K. At temperatures $T \lesssim 50$ K and fields $B \lesssim
1$ T we observe weak anti-localization in the MR; the Hall measurements confirm
the n-type character of the samples. All experimental results of our films are
in quantitative agreement with results from samples prepared using more
sophisticated methods. | 1502.01135v1 |
2015-03-13 | Suspended graphene devices with local gate control on an insulating substrate | We present a fabrication process for graphene-based devices where a graphene
monolayer is suspended above a local metallic gate placed in a trench. As an
example we detail the fabrication steps of a graphene field-effect transistor.
The devices are built on a bare high-resistivity silicon substrate. At
temperatures of 77~K and below, we observe the field-effect modulation of the
graphene resistivity by a voltage applied to the gate. This fabrication
approach enables new experiments involving graphene-based superconducting
qubits and nano-electromechanical resonators. The method is applicable to other
two-dimensional materials. | 1503.04147v2 |
2015-03-18 | A novel fast timing micropattern gaseous detector: FTM | In recent years important progress in micropattern gaseous detectors has been
achieved in the use of resistive material to build compact spark-protected
devices. The novel idea presented here consists of the polarisation of WELL
structures using only resistive coating. This allows a new device to be built
with an architecture based on a stack of several coupled layers where drift and
WELL multiplication stages alternate in the structure. The signals from each
multiplication stage can be read out from any external readout boards through
the capacitive couplings. Each layer provides a signal with a gain of
10^4-10^5. The main advantage of this new device is the dramatic improvement of
the timing provided by the competition of the ionisation processes in the
different drift regions, which can be exploited for fast timing at the high
luminosity accelerators (e.g. HL-LHC upgrade) as well as far applications like
medical imaging. | 1503.05330v1 |
2015-10-19 | High resolution Hall measurements across the VO2 metal-insulator transition reveal impact of spatial phase separation | Many strongly correlated transition metal oxides exhibit a metal-insulator
transition (MIT), the manipulation of which is essential for their application
as active device elements. However, such manipulation is hindered by lack of
microscopic understanding of mechanisms involved in these transitions. A
prototypical example is VO2, where previous studies indicated that the MIT
resistance change correlate with changes in carrier density and mobility. We
studied the MIT using Hall measurements with unprecedented resolution and
accuracy, simultaneously with resistance measurements. Contrast to prior
reports, we find that the MIT is not correlated with a change in mobility, but
rather, is a macroscopic manifestation of the spatial phase separation which
accompanies the MIT. Our results demonstrate that, surprisingly, properties of
the nano-scale spatially-separated metallic and semiconducting domains actually
retain their bulk properties. This study highlights the importance of taking
into account local fluctuations and correlations when interpreting transport
measurements in highly correlated systems. | 1510.05414v1 |
2016-02-12 | Relaxation of the resistive superconducting state in boron-doped diamond films | We report a study of the relaxation time of the restoration of the resistive
superconducting state in single crystalline boron-doped diamond using
amplitude-modulated absorption of (sub-)THz radiation (AMAR). The films grown
on an insulating diamond substrate have a low carrier density of about
2.5x10^{21} cm^{-3} and a critical temperature of about 2 K. By changing the
modulation frequency we find a high-frequency rolloff which we associate with
the characterstic time of energy relaxation between the electron and the phonon
systems or the relaxation time for nonequilibrium superconductivity. Our main
result is that the electron-phonon scattering time varies clearly as T^{-2},
over the accessible temperature range of 1.7 to 2.2 K. In addition, we find,
upon approaching the critical temperature T_c, evidence for an increasing
relaxation time on both sides of T_c. | 1602.04046v1 |
2016-05-12 | Scalable, ultra-resistant structural colors based on network metamaterials | Structural colours have drawn wide attention for their potential as a future
printing technology for various applications, ranging from biomimetic tissues
to adaptive camouflage materials. However, an efficient approach to realise
robust colours with a scalable fabrication technique is still lacking,
hampering the realisation of practical applications with this platform. Here we
develop a new approach based on large scale network metamaterials, which
combine dealloyed subwavelength structures at the nanoscale with loss-less,
ultra-thin dielectrics coatings. By using theory and experiments, we show how
sub-wavelength dielectric coatings control a mechanism of resonant light
coupling with epsilon-near-zero (ENZ) regions generated in the metallic
network, manifesting the formation of highly saturated structural colours that
cover a wide portion of the spectrum. Ellipsometry measurements report the
efficient observation of these colours even at angles of $70$ degrees. The
network-like architecture of these nanomaterials allows for high mechanical
resistance, which is quantified in a series of nano-scratch tests. With such
remarkable properties, these metastructures represent a robust design
technology for real-world, large scale commercial applications. | 1605.03700v1 |
2016-08-02 | Low-energy electron-irradiation effect on transport properties of graphene field effect transistor | We study the effects of low-energy electron beam irradiation up to 10 keV on
graphene based field effect transistors. We fabricate metallic bilayer
electrodes to contact mono- and bi-layer graphene flakes on SiO$_2$, obtaining
specific contact resistivity $\rho_c \simeq 19 k\Omega \mu m^2$ and carrier
mobility as high as 4000 cm$^2$V$^{-1}$s$^{-1}$. By using a highly doped
p-Si/SiO$_2$ substrate as back gate, we analyze the transport properties of the
device and the dependence on the pressure and on the electron bombardment. We
demonstrate that low energy irradiation is detrimental on the transistor
current capability, resulting in an increase of the contact resistance and a
reduction of the carrier mobility even at electron doses as low as 30
$e^-/nm^2$. We also show that the irradiated devices recover by returning to
their pristine state after few repeated electrical measurements. | 1608.00716v1 |
2016-08-23 | Disorder effect on the anisotropic resistivity of phosphorene determined by a tight-binding model | In this work we develop a compact multi-orbital tight-binding model for
phosphorene that accurately describes states near the main band gap. The model
parameters are adjusted using as reference the band structure obtained by a
density-functional theory calculation with the hybrid HSE06 functional. We use
the optimized tight-binding model to study the effects of disorder on the
anisotropic transport properties of phosphorene. In particular, we evaluate how
the longitudinal resistivity depends on the lattice orientation for two typical
disorder models: dilute scatterers with high potential fluctuation amplitudes,
mimicking screened charges in the substrate, and dense scatterers with lower
amplitudes, simulating weakly bounded adsorbates. We show that the intrinsic
anisotropy associated to the band structure of this material, although
sensitive to the type and intensity of the disorder, is robust. | 1608.06633v2 |
2016-10-21 | Giant Positive Magnetoresistance and field-induced metal insulator transition in Cr2NiGa | We report here the magneto-transport properties of the newly synthesized
Heusler compound Cr2NiGa which crystallizes in a disordered cubic B2 structure
belonging to Pm-3m space group. The sample is found to be paramagnetic down to
2 K with metallic character. On application of magnetic field, a significantly
large increase in resistivity is observed which corresponds to
magnetoresistance as high as 112% at 150 kOe of field at the lowest
temperature. Most remarkably, the sample shows negative temperature coefficient
of resistivity below about 50 K under the application of field gretare than or
equal to 80 kOe, signifying a field-induced metal to `insulating' transition.
The observed magnetoresistance follows Kohler's rule below 20 K indicating the
validity of the semiclassical model of electronic transport in metal with a
single relaxation time. A multi-band model for electronic transport, originally
proposed for semimetals, is found to be appropriate to describe the
magneto-transport behavior of the sample. | 1610.06771v1 |
2017-02-08 | Hall field-induced resistance oscillations in MgZnO/ZnO heterostructures | We report on nonlinear magnetotransport in a two-dimensional electron gas
hosted in a MgZnO/ZnO heterostructure. Upon application of a direct current, we
observe pronounced Hall field-induced resistance oscillations (HIRO) which are
well known from experiments on high-mobility GaAs/AlGaAs quantum wells. The
unique sensitivity of HIRO to the short-range component of the disorder
potential allows us to unambiguously establish that the mobility of our
MgZnO/ZnO heterostructure is limited by impurities residing within or near the
2D channel. Demonstration that HIRO can be realized in a system with a much
lower mobility, much higher density, and much larger effective mass than in
previously studied systems, highlights remarkable universality of the
phenomenon and its great promise to be used in studies of a wide variety of
emerging 2D materials. | 1702.02557v1 |
2017-02-22 | Variable-range-hopping conduction processes in oxygen deficient polycrystalline ZnO films | We have fabricated oxygen deficient polycrystalline ZnO films by the rf
sputtering deposition method. To systematically investigate the charge
transport mechanisms in these samples, the electrical resistivities have been
measured over a wide range of temperature from 300 K down to liquid-helium
temperatures. We found that below about 100 K, the variable-range-hopping (VRH)
conduction processes govern the charge transport properties. In particular, the
Mott VRH conduction process dominates at higher temperatures, while crossing
over to the Efros-Shklovskii (ES) VRH conduction process at lower temperatures.
The crossover occurred at temperatures as high as a few tens degrees Kelvin.
Moreover, the temperature behavior of resistivity over the entire VRH
conduction regime from the Mott-type to the ES-type process can be well
described by a universal scaling law. | 1702.06729v1 |
2017-06-25 | Coherent Interlayer Tunneling and Negative Differential Resistance with High Current Density in Double Bilayer Graphene-WSe2 Heterostructures | We demonstrate gate-tunable resonant tunneling and negative differential
resistance between two rotationally aligned bilayer graphene sheets separated
by bilayer WSe2. We observe large interlayer current densities of 2 uA/um2 and
2.5 uA/um2, and peak-to-valley ratios approaching 4 and 6 at room temperature
and 1.5 K, respectively, values that are comparable to epitaxially grown
resonant tunneling heterostructures. An excellent agreement between theoretical
calculations using a Lorentzian spectral function for the two-dimensional (2D)
quasiparticle states, and the experimental data indicates that the interlayer
current stems primarily from energy and in-plane momentum conserving 2D-2D
tunneling, with minimal contributions from inelastic or non-momentum-conserving
tunneling. We demonstrate narrow tunneling resonances with intrinsic
half-widths of 4 and 6 meV at 1.5 K and 300 K, respectively. | 1706.08034v1 |
2017-09-08 | Coulomb drag and counterflow Seebeck coefficient in bilayer-graphene double layers | We have fabricated bilayer-graphene double layers separated by a thin
($\sim$20 nm) boron nitride layer and performed Coulomb drag and counterflow
thermoelectric transport measurements. The measured Coulomb drag resistivity is
nearly three orders smaller in magnitude than the intralayer resistivities. The
counterflow Seebeck coefficient is found to be well approximated by the
difference between Seebeck coefficients of individual layers and exhibit a peak
in the regime where two layers have opposite sign of charge carriers. The
measured maximum counterflow power factor is $\sim$ 700 $\mu$W/K$^2$cm at room
temperature, promising high power output per mass for lightweight
thermoelectric applications. Our devices open a possibility for exploring the
novel regime of thermoelectrics with tunable interactions between n-type and
p-type channels based on graphene and other two-dimensional materials and their
heterostructures. | 1709.02778v1 |
2017-11-05 | Synthesis of sodium cobaltate Na$_{x}$CoO$_{2}$ single crystals with controlled Na ordering | In this study, we synthesized single crystals of Na$_{x}$CoO$_{2}$ with
$x\sim0.8$ using the optical floating zone technique. A thorough
electrochemical treatment of the samples permitted us to control the
de-intercalation of Na to obtain single crystal samples of stable Na ordered
phases with $x=0.5-0.8$. Comparisons of the bulk magnetic properties with those
observed in the Na ordered powder samples confirmed the high quality of these
single crystal phases. The ab plane resistivity was measured for the Na ordered
samples and it was quite reproducible for different sample batches. The data
were analogous to those found in previous initial experimental studies on
single crystals, but the lower residual resistivity and sharper
anti-ferromagnetic transitions determined for our samples confirmed their
higher quality. | 1711.01611v2 |
2018-01-19 | Nontrivial Metallic State of Molybdenum Disulfide | The electrical conductivity and Raman spectroscopy measurements have been
performed on MoS$_2$ at high pressures up to 90 GPa and variable temperatures
down to 5 K. We find that the temperature dependence of the resistance in a
metallic 2H$_a$ phase has an anomaly (a hump) which shifts with pressure to
higher temperature. Concomitantly, a new Raman phonon mode appears in the
metallic state suggesting that the electrical resistance anomaly may be related
to a structural transformation. We suggest that this anomalous behavior is due
to a charge density wave state, the presence of which is indicative for a
possibility for an emergence of superconductivity at higher pressures. | 1801.06351v1 |
2019-05-23 | Laser machined ultrathin microscale platinum thermometers on transparent oxide substrates | Ultrathin microscale resistive thermometers are of key value to many
applications. Here we have fabricated a laser machined 50 ${\mu}$m wide and 50
nm thick serpentine Pt thin film sensor capable of sensing temperatures up to
650 ${^\circ}$ C over multiple heating and cooling cycles. Various materials
and associated processing conditions were studied, including both sapphire and
silica as transparent substrates, alumina and TiO2 as adhesion layers, and
lastly alumina and silicon oxide as capping layer. In-situ resistance
monitoring helps to verify the multi-cycle stability of the sensor and guide
the optimization. 10 ${\mu}$m sized sensors can be laser machined but will not
survive multiple heating and cooling cycles. We demonstrate that the sensors
with amorphous Ge thin layers can also repeatably measure temperatures up to
650 ${^\circ}$ C. It is anticipated that this sensor can be used for fast and
high spatial resolution temperature probing for laser processing applications. | 1905.09812v1 |
2014-08-06 | Desarrollo de capas de AlN sobre aleaciones de aluminio como protección superficial contra la corrosión y el desgaste | Aluminum and their alloys, after careful treatments, can develop excellent
mechanical, tribological, electrical and chemical (high corrosion resistance)
properties. However, 7000 series, with Cu in the alloy, have a poor corrosion
resistance. On the other hand, aluminum nitride (AlN) has a wurtzitic phase and
good thermal stability, optical, electric, piezoelectric, mechanical,
tribological, and chemical properties, so the application range is huge. In
this paper, AlN deposition on Al 7075 was done using the reactive magnetron
sputtering technique in order to verify the aluminum nitride performance as an
Al alloy protective film under wear and corrosive processes. | 1408.1378v1 |
2014-08-28 | Magneto-Dielectric Behavior in $La_{0.53}Ca_{0.47}MnO_{3}$ | We prospect magneto-dielectricity in $La_{0.53}Ca_{0.47}MnO_{3}$ across its
paramagnetic (PMI) to ferromagnetic (FMM) isostructural transition at $T_{C}
\sim 253K$, by magnetic ($(M)$), caloric ($(W)$), dielectric ($(\epsilon')$),
magneto-resistive (MR), and magneto-capacitance (MC) investigations.
Skew-broadened first-order transition character is confirmed via
heating/cooling hystereses in $(M)(T)$ and $(W)(T)$, with superheating
temperature $T**$ almost next to $T_C$ and supercooling temperature $T*$
exhibiting kinetics. Above $T_C$, linearly-related MC and MR reflect purely
magneto-resistance effect. Near $T_C$, the high-frequency MC(5T) much exceeds
the magneto-losses, and is uncorrelated with dc MR(5T) in the FM-ordered state.
The intrinsic magneto-dielectricity manifest below $T_C$ and above ~kHz is
traced to an intra-granular Maxwell-Wagner-type effect at the interface-region
of PMI-FMM phase-coexistence. | 1408.6640v2 |
2017-03-02 | Thermal conduction across a boron nitride and silicon oxide interface | The needs for efficient heat removal and superior thermal conduction in
nano/micro devices have triggered tremendous studies in low-dimensional
materials with high thermal conductivity. Hexagonal boron nitride (h-BN) is
believed to be one of the candidates for thermal management and heat
dissipation due to its novel physical properties, i.e. thermal conductor and
electrical insulator. Here we reported interfacial thermal resistance between
few-layer h-BN and its silicon oxide substrate using differential 3 omega
method. The measured interfacial thermal resistance is around ~1.6*10-8 m2K/W
for monolayer h-BN and ~3.4*10-8 m2K/W for 12.8nm-thick h-BN in metal/h-BN/SiO2
interfaces. Our results suggest that the voids and gaps between substrate and
thick h-BN flakes limit the interfacial thermal conduction. This work provides
a deeper understanding of utilizing h-BN flake as lateral heat spreader in
electronic and optoelectronic nano/micro devices with further miniaturization
and integration. | 1703.00669v1 |
2019-02-10 | The role of plastic strain gradients in the crack growth resistance of metals | Crack advance from short or long pre-cracks is predicted by the progressive
failure of a cohesive zone in a strain gradient, elasto-plastic solid. The
presence of strain gradients leads to the existence of an elastic zone at the
tip of a stationary crack, for both the long crack and the short crack cases.
This is in sharp contrast with previous asymptotic analyses of gradient solids,
where elastic strains were neglected. The presence of an elastic singularity at
the crack tip generates stresses which are sufficiently high to activate
quasi-cleavage. For the long crack case, crack growth resistance curves are
predicted for a wide range of ratios of cohesive zone strength to yield
strength. Remarkably, this feature of an elastic singularity is preserved for
short cracks, leading to a severe reduction in tensile ductility. In
qualitative terms, these predictions resemble those of discrete dislocation
calculations, including the concept of a dislocation-free zone at the crack
tip. | 1902.03664v1 |
2019-07-11 | Impurity concentration dependent electrical conduction in germanium crystal at low temperatures | Germanium single crystal having 45 mm diameter and 100 mm length of 7N+
purity has been grown by Czochralski method. Structural quality of the crystal
has been characterized by Laue diffraction. Electrical conduction and Hall
measurements are carried out on samples retrieved from different parts of the
crystal along the growth axis. Top part of the crystal exhibits lowest impurity
concentration (~10^12/cm3) that gradually increases towards the bottom
(10^13/cm3). The crystal is n-type at room temperature and the resistivity
shows non-monotonic temperature dependence. There is a transition from n-type
to p-type conductivity below room temperature at which bulk resistivity shows
maximum and dip in carrier mobility. This intrinsic to extrinsic transition
regions shift towards room temperature as the impurity concentration increases
and reflects the purity level of the crystal. Similar trend is observed in
boron implanted high purity germanium (HPGe) crystal at different doping level.
The phenomena can be understood as a result of interplay between temperature
dependent conduction mechanism driven by impurity band and intrinsic carrier in
Ge crystals having fairly low acceptor concentrations (<10^12/cm3). | 1907.05067v1 |
2020-02-25 | Non-invasive nanoscale potentiometry and ballistic transport in epigraphene nanoribbons | The recent observation of non-classical electron transport regimes in
two-dimensional materials has called for new high-resolution non-invasive
techniques to locally probe electronic properties. We introduce a novel hybrid
scanning probe technique to map the local resistance and electrochemical
potential with nm- and $\mu$V resolution, and we apply it to study epigraphene
nanoribbons grown on the sidewalls of SiC substrate steps. Remarkably, the
potential drop is non uniform along the ribbons, and $\mu$m-long segments show
no potential variation with distance. The potential maps are in excellent
agreement with measurements of the local resistance. This reveals ballistic
transport in ambient condition, compatible with micrometer-long
room-temperature electronic mean free paths. | 2002.11024v1 |
2020-04-07 | Multi-terminal electronic transport in boron nitride encapsulated TiS$_3$ nanosheets | We have studied electrical transport as a function of carrier density,
temperature and bias in multi-terminal devices consisting of hexagonal boron
nitride (h-BN) encapsulated titanium trisulfide (TiS$_3$) sheets. Through the
encapsulation with h-BN, we observe metallic behavior and high electron
mobilities. Below $\sim$60 K an increase in the resistance, and non-linear
transport with plateau-like features in the differential resistance are
present, in line with the expected charge density wave (CDW) formation.
Importantly, the critical temperature and the threshold field of the CDW phase
can be controlled through the back-gate. | 2004.03687v1 |
2020-04-09 | Magnetic field-dependent resistance crossover and logarithmic to non-saturating magnetoresistance in topological insulator Bi$_2$Te$_3$ | We report a metal-insulator like transition in single crystalline 3D
topological insulator Bi2Te3 at a temperature of 230K in presence of an
external magnetic field applied normal to the surface. This transition becomes
more prominent at larger magnetic field strength with the residual resistance
value increasing linearly with the magnetic field. At low temperature, the
magnetic field dependence of the magnetoresistance shows a transition from
logarithmic to linear behavior and the onset magnetic field value for this
transition decreases with increasing temperature. The logarithmic
magnetoresistance indicates the weak anti-localization of the surface Dirac
electrons while the high temperature behavior originates from the bulk carriers
due to intrinsic impurities. At even higher temperatures beyond~230 K, a
completely classical Lorentz model type quadratic behavior of the
magnetoresistance is observed. We also show that the experimentally observed
anomalies at ~230K in the magneto-transport properties do not originate from
any stacking fault in Bi2Te3. | 2004.04375v2 |
2012-01-02 | Magnetodielectric behavior in La2CoMnO6 nanoparticles | We have investigated magnetic, dielectric and magnetodielectric properties of
La2CoMnO6 nanoparticles prepared by sol-gel method. Magnetization measurements
revealed two distinct ferromagnetic transitions at 218 K and 135 K that can be
assigned to ordered and disordered magnetic phases of the La2CoMnO6
nanoparticles. Two dielectric relaxations culminating around the magnetic
transitions were observed with a maximum magnetodielectric response reaching
10% and 8% at the respective relaxation peaks measured at 100 kHz under 5T
magnetic field. The dc electrical resistivity followed an insulating behavior
and showed a negative magnetoresistance; there was no noticeable anomaly in
resistivity or magnetoresistance near the magnetic ordering temperatures.
Complex impedance analysis revealed a clear intrinsic contribution to the
magnetodielectric response; however, extrinsic contribution due to
Maxwell-Wagner effect combined with magnetoresistance property dominated the
magnetodielectric effect at high temperatures. | 1201.0448v1 |
2012-01-30 | Unusual size effects on thermoelectricity in a strongly correlated oxide | We investigated size effects on thermoelectricity in thin films of a strongly
correlated layered cobaltate. At room temperature, the thermopower is
independent of thickness down to 6 nm. This unusual behavior is inconsistent
with the Fuchs-Sondheimer theory, which is used to describe conventional metals
and semiconductors, and is attributed to the strong electron correlations in
this material. Although the resistivity increases, as expected, below a
critical thickness of $\sim$ 30 nm. The temperature dependent thermopower is
similar for different thicknesses but resistivity shows systematic changes with
thickness. Our experiments highlight the differences in thermoelectric behavior
of strongly correlated and uncorrelated systems when subjected to finite size
effects. We use the atomic limit Hubbard model at the high temperature limit to
explain our observations. These findings provide new insights on decoupling
electrical conductivity and thermopower in correlated systems. | 1201.6274v1 |
2016-03-05 | MIRO-like oscillations of magneto-resistivity in GaAs heterostructures induced by THz radiation | We report on the study of terahertz radiation induced MIRO-like oscillations
of magneto-resistivity in GaAs heterostructures. Our experiments provide an
answer on two most intriguing questions - effect of radiation helicity and the
role of the edges - yielding crucial information for understanding of the MIRO
origin. Moreover, we demonstrate that the range of materials exhibiting
radiation-induced magneto-oscillations can be largely extended by using
high-frequency radiation. | 1603.01760v1 |
2017-05-17 | Epitaxial electrical contact to graphene on SiC | Establishing good electrical contacts to nanoscale devices is a major issue
for modern technology and contacting 2D materials is no exception to the rule.
One-dimensional edge-contacts to graphene were recently shown to outperform
surface contacts but the method remains difficult to scale up. We report a
resist-free and scalable method to fabricate few graphene layers with
electrical contacts in a single growth step. This method derives from the
discovery reported here of the growth of few graphene layers on a metallic
carbide by thermal annealing of a carbide forming metallic film on SiC in high
vacuum. We exploit the combined effect of edge-contact and partially-covalent
surface epitaxy between graphene and the metallic carbide to fabricate devices
in which low contact-resistance and Josephson effect are observed. Implementing
this approach could significantly simplify the realization of large-scale
graphene circuits. | 1705.08257v2 |
2017-07-10 | Phonon-Driven Electron Scattering and Magnetothermoelectric Effect in Two-Dimensional Tin Selenide | The bulk tin selenide (SnSe) is the best thermoelectric material currently
with the highest figure-of-merit due to the strong phonon-phonon interactions.
We investigate the effect of electron-phonon coupling (EPC) on the transport
properties of two-dimensional (2D) SnSe sheet. We demonstrate that EPC plays a
key role in the scattering rate where the constant relaxation time
approximation is deficient. The EPC strength is especially large in contrast to
that of pristine graphene. The scattering rate depends sensitively on the
system temperatures and the carrier densities when the Fermi energy approaches
the band edge. We also investigate the magnetothermoelectric effect of the 2D
SnSe. It is found that at low temperatures there are enormous magnetoelectrical
resistivity and magnetothermal resistivity above 500\%, suggesting the high
potential for device applications. Our results agree reasonably well with the
experimental data. | 1707.02737v1 |
2019-03-05 | Development of a time projection chamber with a sheet-resistor field cage | A new-concept time projection chamber (TPC) using a commercial resistive
sheet, sheet-resistor micro-TPC SR-microPIC, was developed and its performance
was measured. SR-microTPC has the potential to create a more uniform electric
field than conventional TPCs with resistor-chains owing to its continuous sheet
resistivity, and its production would be easier than that of conventional TPCs.
The material used in this study, Achilles-Vynilas, was found to be thin,
transparent, and low-radioactive. The performance test with cosmic muons showed
very promising results, including the demonstration of a good
tracking-performance. This type of TPC field cage can offer an alternative for
the widely used conventional field cages | 1903.01663v3 |
2019-03-30 | Disentangling spin-orbit coupling and local magnetism in a quasi-two-dimensional electron system | Quantum interference between time-reversed electron paths in two dimensions
leads to the well-known weak localization correction to resistance. If
spin-orbit coupling is present, the resistance correction is negative, termed
weak anti-localization (WAL). Here we report the observation of WAL coexisting
with exchange coupling between itinerant electrons and localized magnetic
moments. We use low-temperature magneto-transport measurements to investigate
the quasi-two-dimensional, high-electron-density interface formed between
SrTiO$_3$ (STO) and the anti-ferromagnetic Mott insulator NdTiO$_3$ (NTO). As
the magnetic field angle is gradually tilted away from the sample normal, the
data reveals the interplay between strong $k$-cubic Rashba-type spin-orbit
coupling and a substantial magnetic exchange interaction from local magnetic
regions. The resulting quantum corrections to the conduction are in excellent
agreement with existing models and allow sensitive determination of the small
magnetic moments (22 $\mu_B$ on average), their magnetic anisotropy and mutual
coupling strength. This effect is expected to arise in other 2D magnetic
materials systems. | 1904.00295v2 |
2019-08-27 | Large surface conductance and two-dimensional superconductivity in microstructured crystalline topological insulators | Controllable geometric manipulation via micromachining techniques provides a
promising tool for enhancing useful topological electrical responses relevant
to future applications such as quantum information science. Here we present
microdevices fabricated with focused ion beam from indium-doped topological
insulator Pb1-xSnxTe. With device thickness on the order of 1 {\mu}m and an
extremely large bulk resistivity, we achieve an unprecedented enhancement of
the surface contribution to about 30% of the total conductance near room
temperature. The surface contribution increases as the temperature is reduced,
becoming dominant below approximately 180 K, compared to 30 K in mm-thickness
crystals. In addition to the enhanced surface contribution to normal-state
transport, we observe the emergence of a two-dimensional superconductivity
below 6 K. Measurements of magnetoresistivity at high magnetic fields reveal a
weak antilocalization behavior in the normal-state magnetoconductance at low
temperature and a variation in the power-law dependence of resistivity on
temperature with field. These results demonstrate that interesting electrical
response relevant to practical applications can be achieved by suitable
engineering of single crystals. | 1908.10427v1 |
2019-12-11 | Pressure-induced superconductivity and structural transition in ferromagnetic Cr2Si2Te6 | The discovery of intrinsic magnetism in atomically thin two-dimensional
transition-metal trichalcogenides has attracted intense research interest due
to the exotic properties of magnetism and potential applications in devices.
Pressure has proven to be an effective tool to manipulate the crystal and
electronic structures of the materials. Here, we report investigations on
ferromagnetic van der Waals Cr2Si2Te6 via high-pressure synchrotron x-ray
diffraction, electrical resistance, Hall resistance, and magnetoresistance
measurements. Under compression, Cr2Si2Te6 simultaneously undergoes a
structural transition, emergence of superconductivity at 3 K, sign change of
the magnetoresistance, and dramatic change of the Hall coefficient at ~8 GPa.
The superconductivity persists up to the highest measured pressure of 47.1 GPa
with a maximum Tc = 4.5 K at ~30 GPa. The discovery of superconductivity in the
two-dimensional van der Waals ferromagnetic Cr-based Cr2Si2Te6 provides new
perspectives to explore superconductivity and the interplay between
superconductivity and magnetism. | 1912.05166v1 |
2012-06-23 | Molecular-beam epitaxial growth of a far-infrared transparent electrode for extrinsic Germanium photoconductors | We have evaluated the optical and electrical properties of a far-infrared
(IR) transparent electrode for extrinsic germanium (Ge) photoconductors at 4 K,
which was fabricated by molecular beam epitaxy (MBE). As a far-IR transparent
electrode, an aluminum (Al)-doped Ge layer is formed at well-optimized doping
concentration and layer thickness in terms of the three requirements: high
far-IR transmittance, low resistivity, and excellent ohmic contact. The
Al-doped Ge layer has the far-IR transmittance of >95 % within the wavelength
range of 40--200 microns, while low resistivity (~5 ohm-cm) and ohmic contact
are ensured at 4 K. We demonstrate the applicability of the MBE technology in
fabricating the far-IR transparent electrode satisfying the above requirements. | 1206.5368v1 |
2015-04-08 | Post-growth purification of Co nanostructures prepared by focused electron beam induced deposition | In the majority of cases nanostructures prepared by focused electron beam
induced deposition (FEBID) employing an organometallic precursor contain
predominantly carbon-based ligand dissociation products. This is unfortunate
with regard to using this high-resolution direct-write approach for the
preparation of nanostructures for various fields, such as mesoscopic physics,
micromagnetism, electronic correlations, spin-dependent transport and numerous
applications. Here we present an in-situ cleaning approach to obtain pure
Co-FEBID nanostructures. The purification procedure lies in the exposure of
heated samples to a H$_2$ atmosphere in conjunction with the irradiation by
low-energy electrons. The key finding is that the combination of annealing at
$300^\circ$C, H$_2$ exposure and electron irradiation leads to compact, carbon-
and oxygen free Co layers down to a thickness of about 20\,nm starting from
as-deposited Co-FEBID structures. In addition to this, in temperature-dependent
electrical resistance measurements on post-processed samples we find a typical
metallic behavior. In low-temperature magneto-resistance and Hall effect
measurements we observe ferromagnetic behavior. | 1504.01945v1 |
2015-06-22 | Preparation, characterization, and electrical properties of epitaxial NbO2 thin film lateral devices | Epitaxial NbO2 (110) films, 20 nm thick, were grown by pulsed laser
deposition on Al2O3 (0001) substrates. The Ar/O2 total pressure during growth
was varied to demonstrate the gradual transformation between NbO2 and Nb2O5
phases, which was verified using x-ray diffraction, x-ray photoelectron
spectroscopy, and optical absorption measurements. Electric resistance
threshold switching characteristics were studied in a lateral geometry using
interdigitated Pt top electrodes in order to preserve the epitaxial crystalline
quality of the films. Volatile and reversible transitions between high and low
resistance states were observed in epitaxial NbO2 films, while irreversible
transitions were found in case of Nb2O5 phase. Electric field pulsed current
measurements confirmed thermally-induced threshold switching. | 1506.06640v2 |
2018-07-25 | Galvanomagnetic properties of the putative type-II Dirac semimetal PtTe$_2$ | Platinum ditelluride has recently been characterized, based on angle-resolved
photoemission spectroscopy data and electronic band structure calculations, as
a possible representative of type-II Dirac semimetals. Here, we report on the
magnetotransport behavior (electrical resistivity, Hall effect) in this
compound, investigated on high-quality single-crystalline specimens. The
magnetoresistance (MR) of PtTe$_2$ is large (over $3000\%$ at $T=1.8$ K in
$B=9$ T) and unsaturated in strong fields in the entire temperature range
studied. The MR isotherms obey a Kohler's type scaling with the exponent $m$ =
1.69, different from the case of ideal electron-hole compensation. In applied
magnetic fields, the resistivity shows a low-temperature plateau,
characteristic of topological semimetals. In strong fields, well-resolved
Shubnikov - de Haas (SdH) oscillations with two principle frequencies were
found, and their analysis yielded charge mobilities of the order of
$10^3\,\rm{cm^2V^{-1}s^{-1}}$ and rather small effective masses of charge
carriers, $0.11m_e$ and $0.21m_e$. However, the extracted Berry phases point to
trivial character of the electronic bands involved in the SdH oscillations. The
Hall effect data corroborated a multi-band character of the electrical
conductivity in PtTe$_2$, with moderate charge compensation. | 1807.09876v1 |
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