publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2002-07-05 | On the two-dimensional metallic state in silicon-on-insulator structures | It is shown that the electronic conduction in silicon-on-insulator (SOI)
layers exhibits a metallic regime which is very similar to that in
high-mobility Si-metal oxide semiconductor structures (MOS). The peak in the
electron mobility versus density, the strong drop in resistivity and the
critical concentration for the metal-insulator transition are all consistent.
On the basis of our SOI data for the temperature and in-plane magnetic field
dependence of the resistivity, we discuss several models for the metallic state
in two dimensions. We find that the observed behavior can be well described by
the theory on the interaction corrections in the ballistic regime. For the
investigated regime, the temperature dependent screening of scattering
potentials gives also a good description of the data. | 0207170v1 |
2003-01-21 | Angular dependence of domain wall resistivity in SrRuO$_{\bf 3}$ films | ${\rm SrRuO_3}$ is a 4d itinerant ferromagnet (T$_{c}$ $\sim $150 K) with
stripe domain structure. Using high-quality thin films of SrRuO$_{3}$ we study
the resistivity induced by its very narrow ($\sim 3$ nm) Bloch domain walls,
$\rho_{DW}$ (DWR), at temperatures between 2 K and T$_{c}$ as a function of the
angle, $\theta $, between the electric current and the ferromagnetic domains
walls. We find that $\rho_{DW}(T,\theta)=\sin^2\theta
\rho_{DW}(T,90)+B(\theta)\rho_{DW}(T,0)$ which provides the first experimental
indication that the angular dependence of spin accumulation contribution to DWR
is $\sin^2\theta$. We expect magnetic multilayers to exhibit a similar
behavior. | 0301400v2 |
2003-04-30 | Radiation-induced magnetoresistance oscillation in a two-dimensional electron gas in Faraday geometry | Microwave-radiation induced giant magnetoresistance oscillations recently
discovered in high-mobility two-dimensional electron systems in a magnetic
field, are analyzed theoretically. Multiphoton-assisted impurity scatterings
are shown to be the primary origin of the oscillation. Based on a model which
considers the interaction of electrons with the electromagnetic fields in
Faraday geometry, we are able not only to reproduce the correct period, phase
and the negative resistivity of the main oscillation, but also to obtain
secondary peaks and additional maxima and minima in the resistivity curve, some
of which were already observed in the experiments. | 0304687v2 |
2003-06-03 | Signatures of valence fluctuations in CeCu2Si2 under high pressure | Simultaneous resistivity and a.c.-specific heat measurements have been
performed under pressure on single crystalline CeCu2Si2 to over 6 GPa in a
hydrostatic helium pressure medium. A series of anomalies were observed around
the pressure coinciding with a maximum in the superconducting critical
temperature, $T_c^{max}$. These anomalies can be linked with an abrupt change
of the Ce valence, and suggest a second quantum critical point at a pressure
$P_v \simeq 4.5$ GPa, where critical valence fluctuations provide the
superconducting pairing mechanism, as opposed to spin fluctuations at ambient
pressure. Such a valence instability, and associated superconductivity, is
predicted by an extended Anderson lattice model with Coulomb repulsion between
the conduction and f-electrons. We explain the T-linear resistivity found at
$P_v$ in this picture, while other anomalies found around $P_v$ can be
qualitatively understood using the same model. | 0306054v1 |
2003-06-09 | Thermal fluctuations in ultrasmall intrinsic Josephson junctions | Current-voltage curves of small area hysteretic intrinsic Josephson
junctions, for which the Josephson energy $E_J=\hbar J_c/2e$ is of order of
thermal energy $kT$, are investigated. A non-monotonic temperature dependence
of the switching current is observed and explained by thermal phase
fluctuations. At low temperatures premature switching from the superconducting
into the resistive state is the most important effect of fluctuations. At high
temperatures only a single resistive branch is observed. At the cross-over
temperature a hysteretic phase-diffusion branch exists. It shows the importance
of a frequency-dependent impedance of an external circuit formed by the leads. | 0306212v1 |
2003-11-25 | Comparative study of in situ and ex situ MgB2 films deposited by pulsed laser deposition | Two types of MgB2 films were prepared by pulsed laser deposition (PLD) with
in situ and ex situ annealing processes respectively. Significant differences
in properties between the two types of films were found. The ex situ MgB2 film
has a Tc of 38.1K, while the in situ film has a depressed Tc of 34.5K. The
resistivity at 40K for the in situ film is larger than that of the ex situ film
by a factor of 6. The residual resistivity ratios (RRR) are 1.1 and 2.1 for the
in situ and ex situ films respectively. The Jc-H curves of the in situ film
show a much weaker field dependence than those of the ex situ film,
attributable to stronger flux pinning in the in situ film. The small-grain
feature and high oxygen level may be critical for the significant improvement
of Jc in the in situ annealed MgB2 film. | 0311556v1 |
2004-02-12 | Self-localization of holes in a lightly doped Mott insulator | We show that lightly doped holes will be self-trapped in an antiferromagnetic
spin background at low-temperatures, resulting in a spontaneous translational
symmetry breaking. The underlying Mott physics is responsible for such novel
self-localization of charge carriers. Interesting transport and dielectric
properties are found as the consequences, including large doping-dependent
thermopower and dielectric constant, low-temperature variable-range-hopping
resistivity, as well as high-temperature strange-metal-like resistivity, which
are consistent with experimental measurements in the high-T$_c$ cuprates.
Disorder and impurities only play a minor and assistant role here. | 0402327v2 |
2004-03-09 | Resistivity and Thermopower of Ni2.19Mn0.81Ga | In this paper, we report results of the first studies on the thermoelectric
power (TEP) of the magnetic heusler alloy Ni$_{2.19}$Mn$_{0.81}$Ga. We explain
the observed temperature dependence of the TEP in terms of the crystal field
(CF) splitting and compare the observed behavior to that of the stoichiometric
system Ni$_2$MnGa. The resistivity as a function of temperature of the two
systems serves to define the structural transition temperature, T$_M$, which is
the transition from the high temperature austenitic phase to low temperatures
the martensitic phase. Occurrence of magnetic (Curie-Weiss) and the martensitic
transition at almost the same temperature in Ni$_{2.19}$Mn$_{0.81}$Ga has been
explained from TEP to be due to changes in the density of states (DOS) at the
Fermi level. | 0403232v2 |
2004-07-21 | YbNiSi3: a new antiferromagnetic Kondo lattice with strong exchange interaction | We report on the structural, thermodynamic and transport properties of
high-quality single crystals of YbNiSi3 grown by the flux method. This compound
crystallizes in the SmNiGe3 layered structure type of the Cmmm space group. The
general physical behavior is that of a Kondo lattice showing an
antiferromagnetic ground state below T_N = 5.1 K. This is among the highest
ordering temperatures for a Yb-based intermetallic, indicating strong exchange
interaction between the Yb ions, which are close to +3 valency based on the
effective moment of 4.45 mu_B/f.u. The compound has moderately heavy-electron
behavior with Sommerfeld coefficient 190 mJ/mol K^2. Resistivity is highly
anisotropic and exhibits the signature logarithmic increase below a local
minimum, followed by a sharp decrease in the coherent/magnetically ordered
state, resulting in residual resistivity of 1.5 micro Ohm cm and RRR = 40.
Fermi-liquid behavior consistent with a ground-state doublet is clearly
observed below 1 K. | 0407543v1 |
2004-09-05 | Infrared study of giant dielectric constant in Li and Ti doped NiO | We have measured optical reflectivity of Li and Ti doped NiO (LTNO) in the
infrared range at various temperatures. A Drude-like absorption is found at low
energy, $\omega <$ 100 cm$^{-1}$ and its spectral weight increases
substantially as temperature decreases. This observation and DC-resistivity
result show that LTNO has a conductive grain and resistive boundary. Such
composite structure provides evidence of the Maxwell-Wagner (MW) mechanism as
the origin of the high dielectric constant $\epsilon_{o}$. We propose a
three-phase granular structure and show that this extended MW model explains
the observed frequency and temperature dependence of the dielectric constant as
well as the giant value of $\epsilon_{o}$. | 0409105v1 |
2004-09-09 | Anomalous Pressure Dependence of Kadowaki-Woods ratio and Crystal Field Effects in Mixed-valence YbInCu4 | The mixed-valence (MV) compound YbInCu4 was investigated by electrical
resistivity and ac specific heat at low temperatures and high pressures. At
atmospheric pressure, its Kadowaki-Woods (KW) ratio, A/\gamma ^2, is 16 times
smaller than the universal value R_{KW}(=1.0 x 10^-5 \mu \Omega cm mol^2 K^2
mJ^-2), but sharply increases to 16.5R_{KW} at 27 kbar. The pressure-induced
change in the KW ratio and deviation from R_{KW} are analyzed in terms of the
change in f-orbital degeneracy N and carrier density n. This analysis is
further supported by a dramatic change in residual resistivity \rho_0 near 25
kbar, where \rho_0 jumps by a factor of 7. | 0409243v2 |
2004-10-01 | Inherent Relation between Nernst Signal and Nodal Quasiparticle Transport in Pseudogap Region of Underdoped High Temperature Superconductors | In-plane Nernst signal and resistivity have been measured for three
$La_{2-x}Sr_xCuO_4$ single crystals (x=0.09, 0.11 and 0.145) with the magnetic
field parallel to c-axis. A quadratic temperature dependence of resistivity,
i.e., $\rho=\rho_0+aT^2$ is observed below a certain temperature $T_R$. It is
found that the upper boundary of the Nernst signal $T_n$ coincides with $T_R$,
which points to an inherent relation between the anomalous Nernst signal and
the nodal quasiparticle transport in the pseudogap region. Finally a phase
diagram together with the pseudogap temperature $T^*$ is presented, which
suggests a second energy scale in the pseudogap region. | 0410013v2 |
2004-11-23 | Magnetic field-tuned quantum critical point in CeAuSb_2 | Transport, magnetic and thermal properties at high magnetic fields (H) and
low temperatures (T) of the heavy fermion compound CeAuSb_2 are reported. At
H=0 this layered system exhibits antiferromagnetic order below T_N = 6 K.
Applying B along the inter-plane direction, leads to a continuous suppression
of T_N and a quantum critical point at H_c ~ 5.4 T. Although it exhibits Fermi
liquid behavior within the Neel phase, in the paramagnetic state the
fluctuations associated with H_c give rise to unconventional behavior in the
resistivity (sub-linear in T) and to a TlnT dependence in the magnetic
contribution to the specific heat. For H > H_c and low T the electrical
resistivity exhibits an unusual T^3-dependence. | 0411588v2 |
2005-02-14 | Superconductivity induced by spark erosion in ZrZn2 | We show that the superconductivity observed recently in the weak itinerant
ferromagnet ZrZn2 [C. Pfleiderer et al., Nature (London) 412, 58 (2001)] is due
to remnants of a superconducting layer induced by spark erosion. Results of
resistivity, susceptibility, specific heat and surface analysis measurements on
high-quality ZrZn2 crystals show that cutting by spark erosion leaves a
superconducting surface layer. The resistive superconducting transition is
destroyed by chemically etching a layer of 5 microns from the sample. No
signature of superconductivity is observed in rho(T) of etched samples at the
lowest current density measured, J=675 Am-2, and at T < 45 mK. EDX analysis
shows that spark-eroded surfaces are strongly Zn depleted. The simplest
explanation of our results is that the superconductivity results from an alloy
with higher Zr content than ZrZn2. | 0502341v2 |
2005-04-05 | Interaction and disorder in bilayer counterflow transport at filling factor one | We study high mobility, interacting GaAs bilayer hole systems exhibiting
counterflow superfluid transport at total filling factor $\nu=1$. As the
density of the two layers is reduced, making the bilayer more interacting, the
counterflow Hall resistivity ($\rho_{xy}$) decreases at a given temperature,
while the counterflow longitudinal resistivity ($\rho_{xx}$), which is much
larger than $\rho_{xy}$, hardly depends on density. On the other hand, a small
imbalance in the layer densities can result in significant changes in
$\rho_{xx}$ at $\nu=1$, while $\rho_{xy}$ remains vanishingly small. Our data
suggest that the finite $\rho_{xx}$ at $\nu=1$ is a result of mobile vortices
in the superfluid created by the ubiquitous disorder in this system. | 0504119v1 |
2005-05-19 | On the problem of the Kondo-lattice model application to CeB6 | Precision measurements of charge transport parameters (resistivity, Hall and
Seebeck coefficients) have been carried out on high-quality single-crystals of
cerium hexaboride in a wide temperature range 1.8-300 K. It is shown that in
the temperature interval of 5 K < T < T* = 80 K the magnetic contribution in
resistivity obeys the power law rm = T -1/n, which corresponds to the regime of
weak localization of charge carriers with the critical index 1/n = 0.39 +-
0.02. In the same temperature interval an asymptotic behavior of thermopower S
= -lnT is found together with an essential decrease of the charge carriers
mobility in CeB6. A negative Hall coefficient anomaly has been detected at
liquid helium temperatures. The data obtained are compared with the results
predicted by the Kondo-lattice model and discussed also in terms of the theory
of excitonic ferromagnetism. | 0505475v1 |
2005-06-15 | Resistivity study of the pseudogap phase for (Hg,Re) - 1223 superconductors | The pseudogap phase above the critical temperature of high $T_{c}$
superconductors (HTSC) presents different energy scales and it is currently a
matter of intense study. The complexity of the HTSC normal state requires very
accurate measurements with the purpose of distinguishing different types of
phenomena. Here we have performed systematically studies through electrical
resistivity ($\rho$) measurements by several different current densities in
order to obtain an optimal current for each sample. This approach allows to
determine reliable values of the pseudogap temperature $T^{*}(n)$, the layer
coupling temperature between the superconductor layers $T_{LD}(n)$, the
fluctuation temperature $T_{scf}(n)$ and the critical temperature $T_{c}(n)$ as
function of the doping $n$. The interpretation of these different temperature
scales allows to characterize possible scenarios for the (Hg,Re) - 1223 normal
state. This method, described in detail here, and used to derive the
(Hg,Re)-1223 phase diagram is general and can be applied to any HTSC. | 0506387v2 |
2005-08-29 | Universal Minimum Heat Leak on Low-Temperature Metallic Electrical Leads | Low-temperature electronic systems require electrical leads which have low
electrical resistance to provide bias current I without excessive voltage drop
V. But proper cryogenic design also requires high thermal resistance to
maintain a minimum heat leak Q from the hot temperature T[hot] to the cold
temperature T[cold]. By the Wiedemann-Franz law, these requirements are in
direct conflict, and the optimal configuration takes a particularly simple
universal approximate form for the common case that T[cold] << T[hot]: Q/I = V
= 3.6 kT[hot]/e. This is applied here to the cryopackaging of RSFQ
superconducting circuits on a 4K cryocooler, but is equally applicable to other
cryogenic systems such as a superconducting sensor array at low and ultra-low
temperatures. | 0508697v2 |
2005-09-01 | Comment on "Magnetic quantum oscillations of the conductivity in layered conductors" | We discuss the recent theory of Gvozdikov [Phys. Rev. B 70, 085113 (2004)]
which aims at explaining the Shubnikov-de Haas oscillations of the longitudinal
resistivity \rho_zz observed in the quasi-two-dimensional organic compound
\beta''-(BEDT-TTF)_2SF_5CH_2CF_2SO_3.
We point out that the self-consistent equations of the theory yielding the
longitudinal resistivity and the magnetic field dependence of the chemical
potential have been incorrectly solved. We show that the consideration of the
self-consistent Born approximation (which determines the relaxation rate in
Gvozdikov's paper) leads in fact to the complete absence of the longitudinal
conductivity \sigma_{zz} at leading order in high magnetic fields. | 0509026v2 |
2005-10-14 | Ferromagnetic Properties of ZrZn$_2$ | The low Curie temperature (T_C approx 28K) and small ordered moment (M_0
approx 0.17 mu_B f.u.^-1) of ZrZn2 make it one of the few examples of a weak
itinerant ferromagnet. We report results of susceptibility, magnetization,
resistivity and specific heat measurements made on high-quality single crystals
of ZrZn2. From magnetization scaling in the vicinity of T_C
(0.001<|T-T_C|/T_C<0.08), we obtain the critical exponents beta=0.52+/-0.05 and
delta=3.20+/-0.08, and T_C=27.50+/-0.05K. Low-temperature magnetization
measurements show that the easy axis is [111]. Resistivity measurements reveal
an anomaly at T_C and a non-Fermi liquid temperature dependence
rho(T)=rho_0+AT^n, where n=1.67+/-0.02, for 1<T<14K. The specific heat
measurements show a mean-field-like anomaly at T_C. We compare our results to
various theoretical models. | 0510384v1 |
2005-12-23 | Spin-charge gauge symmetry: A way to tackle HTS cuprates? | We propose an explanation of several experimental features of transport
phenomena in the normal state of high Tc cuprates in terms of a spin-charge
gauge theory of the 2D t-J model. The calculated doping-temperature dependence
for a number of physical quantities is found in qualitative agreement with
data. In particular, we recover: in the ``pseudogap phase'' the metal-insulator
crossover of the in-plane resistivity and of the NMR ``relaxation time'' and
the insulating behavior of the out-of-plane resistivity; in the ``strange metal
phase'' (at higher temperature or doping) the linear in T behavior of the above
quantities; the appearance of maxima in the in-plane far-infrared conductivity
in strongly underdoped and overdoped samples. | 0512607v1 |
2006-02-01 | Coulomb blockade and transport in a chain of one-dimensional quantum dots | A long one-dimensional wire with a finite density of strong random impurities
is modelled as a chain of weakly coupled quantum dots. At low temperature T and
applied voltage V its resistance is limited by "breaks": randomly occuring
clusters of quantum dots with a special length distribution pattern that
inhibits the transport. Due to the interplay of interaction and disorder
effects the resistance can exhibit T and V dependences that can be approximated
by power laws. The corresponding two exponents differ greatly from each other
and depend not only on the intrinsic electronic parameters but also on the
impurity distribution statistics. | 0602008v3 |
2006-02-14 | Intrinsic nonlinearity probed by intermodulation distortion microwave measurements on high quality MgB2 thin films | The two tone intermodulation distortion arising in MgB2 thin films
synthesized by hybrid physical-chemical vapour deposition is studied in order
to probe the influence of the two bands on the nonlinear response of this
superconductor. The measurements are carried out by using a dielectrically
loaded copper cavity operating at 7 GHz. Microwave data on samples having
critical temperatures above 41 K, very low resistivity values, and residual
resistivity ratio larger than 10, are shown. The dependence of the nonlinear
surface losses and of the third order intermodulation products on the power
feeding the cavity and on the temperature is analyzed. At low power, the signal
arising from distortion versus temperature shows the intrinsic s-wave behavior
expected for this compound. Data are compared with measurements performed on Nb
and YBCO thin films using the same technique. | 0602340v1 |
2006-02-21 | Evidence of s-wave pairing symmetry in layered superconductor Li$_{0.68}$NbO$_2$ from the specific heat measurement | A high quality superconducting Li$_{0.68}$NbO$_2$ polycrystalline sample was
synthesized by deintercalation of Li ions from Li$_{0.93}$NbO$_2$. The field
dependent resistivity and specific heat were measured down to 0.5 K. The upper
critical field $H_{c2} (T)$ is deduced from the resistivity data and
$H_{c2}(0)$ is estimated to be $\sim 2.98$ T. A notable specific heat jump is
observed at the superconducting transition temperature $T_c \sim 5.0$ K at zero
field. Below $T_c$, the electronic specific heat shows a thermal activated
behavior and agrees well with the theoretical result of the BCS s-wave
superconductors. It indicates that the superconducting pairing in
Li$_{0.68}$NbO$_2$ has s-wave symmetry. | 0602476v1 |
2006-03-29 | Resistivity and Magneto-Optical Evidence for Variable and Incomplete Connectivity in Dense, High Critical Current Density C-alloyed Magnesium Diboride | Carbon-doped magnesium diboride was fabricated from pre-reacted pure MgB2 by
mechanical alloying. The sample set had excellent critical current densities
Jc(8T,4.2K) ranging from 15-60 kA/cm2, depending on composition.
Magneto-optical imaging detected regions up to 0.5 mm in size which were nearly
100% dense with Jc 2-6 times that of the matrix. Evaluation of resistivity
curves using the Rowell method predicts that only 10-50% of the cross sectional
area carries the normal state measurement current, suggesting that considerable
increases in Jc in these ~80% dense MgB2 samples would be possible with
complete grain and particle connectivity. | 0603800v1 |
2006-06-08 | Periodic Oscillations of Josephson-Vortex Flow Resistance in Oxygen-Deficient Y1Ba2Cu3Ox | We measured the Josephson vortex flow resistance as a function of magnetic
field applied parallel to the ab-planes using annealed Y1Ba2Cu3Ox intrinsic
Josephson junctions having high anisotropy (around 40) by oxygen content
reduction. Periodic oscillations were observed in magnetic fields above 45-58
kOe, corresponding to dense-dilute boundary for Josephson vortex lattice. The
observed period of oscillations, agrees well with the increase of one fluxon
per two junctions ($H_{p}$\textit{=$\Phi $}$_{0}$\textit{/2Ls}), may correspond
to formation of a triangular lattice of Josephson vortices as has been reported
by Ooi et al. for highly anisotropic (larger than 200) Bi-2212 intrinsic
Josephson junctions. | 0606202v2 |
2006-06-26 | Flux-flow resistivity anisotropy in the instability regime in the a-b plane of epitaxial YBCO thin films | Measurements of the nonlinear flux-flow resistivity $\rho$ and the critical
vortex velocity $\rm v^*_\phi$ at high voltage bias close to the instability
regime predicted by Larkin and Ovchinnikov \cite{LO} are reported along the
node and antinode directions of the d-wave order parameter in the \textit{a-b}
plane of epitaxial $YBa_2Cu_3O_{7-\delta}$ films. In this pinning-free regime,
$\rho$ and $\rm v^*_\phi$ are found to be anisotropic with values in the node
direction larger on average by 10% than in the antinode direction. The
anisotropy of $\rho$ is almost independent of temperature and field. We
attribute the observed results to the anisotropic quasiparticle distribution on
the Fermi surface of $YBa_2Cu_3O_{7-\delta}$. | 0606667v1 |
2006-07-01 | Nonlocal Effect of Local Nonmagnetic Impurity in High-Tc Superconductors: Induced Local Moment and Huge Residual Resistivity | We study a Hubbard model with a strong onsite impurity potential based on an
improved fluctuation-exchange (FLEX) approximation, which we call the GVI-FLEX
method. We find that (i) both local and staggered susceptibilities are strongly
enhanced around the impurity. By this reason, (ii) the quasiparticle lifetime
as well as the local density of states (DOS) are strongly suppressed in a wide
area around the impurity (like a Swiss cheese hole), which causes the ``huge
residual resistivity'' beyond the s-wave unitary scattering value. These
results by the GVI method naturally explains the various impurity effects in
HTSC's in a unified way, which had been a long-standing theoretical problem. | 0607011v1 |
2006-07-21 | Vortex state microwave resistivity in Tl-2212 thin films | We present measurements of the field induced changes in the 47 GHz complex
resistivity, $\Delta \tilde \rho(H,T)$, in Tl$_{2}$Ba$_{2}$CaCu$_{2}$O$_{8+x}$
(TBCCO) thin films with $T_{c}\simeq$ 105 K, prepared on CeO$_{2}$ buffered
sapphire substrates. At low fields ($\mu_{0}H<$10 mT) a very small irreversible
feature is present, suggesting a little role of intergranular phenomena. Above
that level $\Delta \tilde \rho(H,T)$ exhibits a superlinear dependence with the
field, as opposed to the expected (at high frequencies) quasilinear behaviour.
We observe a crossover between predominantly imaginary to predominantly real
(dissipative) response with increasing temperature and/or field. In addition,
we find the clear scaling property $\Delta \tilde \rho(H,T)=\Delta \tilde
\rho[H/H^{*}(T)]$, where the scaling field $H^{*}(T)$ maps closely the melting
field measured in single crystals. We discuss our microwave results in terms of
loss of flux lines rigidity. | 0607552v1 |
2006-08-31 | Magnetotransport in a two-dimensional electron system in dc electric fields | We report on nonequilibrium transport measurements in a high-mobility
two-dimensional electron system subject to weak magnetic field and dc
excitation. Detailed study of dc-induced magneto-oscillations, first observed
by Yang {\em et al}., reveals a resonant condition that is qualitatively
different from that reported earlier. In addition, we observe dramatic
reduction of resistance induced by a weak dc field in the regime of separated
Landau levels. These results demonstrate similarity of transport phenomena in
dc-driven and microwave-driven systems and have important implications for
ongoing experimental search for predicted quenching of microwave-induced
zero-resistance states by a dc current. | 0608727v3 |
2006-10-04 | Quantum phase transition in the heavy-fermion compound YbIr$_2$Si$_2$ | We investigate the pressure-temperature phase diagram of YbIr$_2$Si$_2$ by
measuring the electrical resistivity $\rho(T)$. In contrast to the widely
investigated YbRh$_2$Si$_2$, YbIr$_2$Si$_2$ is a paramagnetic metal below
$p_c\simeq 8$ GPa. Interestingly, a first-order, presumably ferromagnetic,
transition develops at $p_c$. Similar magnetic properties were also observed in
YbRh$_2$Si$_2$ and YbCu$_2$Si$_2$ at sufficiently high pressures, suggesting a
uniform picture for these Yb compounds. The ground state of YbIr$_2$Si$_2$
under pressure can be described by Landau Fermi-liquid (LFL) theory, in
agreement with the nearly ferromagnetic Fermi-liquid (NFFL) model. Moreover,
evidence of a weak valence transition, characterized by a jump of the
Kadowaki-Woods (KW) ratio as well as an enhancement of the residual resistivity
$\rho_0$ and of the quasiparticle-quasiparticle scattering cross section, is
observed around 6 GPa. | 0610126v1 |
2006-11-09 | Small-angle interband scattering as the origin of the $T^{3/2}$ resistivity in MnSi | A possible explanation is given for the anomalous $T^{3/2}$ temperature
dependence of the electrical resistivity of MnSi, which is observed in the
high-pressure paramagnetic state. The unusual Fermi surface of MnSi includes
large open sheets that intersect along the faces of the cubic Brillouin zone.
Close to these intersections, long-wavelength interband magnetic spin
fluctuations can scatter electrons from one sheet to the other. The current
relaxation rate due to such interband scattering events is not reduced by
vertex corrections as is that for scattering from intraband ferromagnetic
fluctuations. Consequently, current relaxation proceeds in a manner similar to
that occurring in nearly antiferromagnetic metals, in which low-temperature
$T^{3/2}$ behavior is well known. It is argued that this type of
non-Fermi-liquid behavior can, for a metal with ferromagnetic fluctuations near
Fermi sheet intersections, persist over a much wider temperature range than it
does in nearly antiferromagnetic metals. | 0611236v1 |
2006-12-22 | Transport through normal metal - graphene contacts | Conductance of zigzag interfaces between graphene sheet and normal metal is
investigated in the tight-binding approximation. Boundary conditions, valid for
a variety of scattering problems, are constructed and applied to the normal
metal -- graphene -- normal metal (NGN) junctions. At the Dirac point, the
conductance is determined solely by the evanescent modes and is inversely
proportional to the length of the junction. It is also independent on the
interface resistance. Away from the Dirac point, the propagating modes'
contribution dominates. We also observe that even in the junctions with high
interface resistance, for certain modes, ideal transmission is possible via
Fabry-Perot like resonances. | 0612577v3 |
2007-01-04 | Anomalous Hall Resistance in Bilayer Quantum Hall Systems | We present a microscopic theory of the Hall current in the bilayer quantum
Hall system on the basis of noncommutative geometry. By analyzing the
Heisenberg equation of motion and the continuity equation of charge, we
demonstrate the emergence of the phase current in a system where the interlayer
phase coherence develops spontaneously. The phase current arranges itself to
minimize the total energy of the system, as induces certain anomalous behaviors
in the Hall current in the counterflow geometry and also in the drag
experiment. They explain the recent experimental data for anomalous Hall
resistances due to Kellogg et al. [M. Kellogg, I.B. Spielman, J.P. Eisenstein,
L.N. Pfeiffer and K.W. West, Phys. Rev. Lett. \textbf{88} (2002) 126804; M.
Kellogg, J.P. Eisenstein, L.N. Pfeiffer and K.W. West, Phys. Rev. Lett.
\textbf{93} (2004) 036801] and Tutuc et al. [E. Tutuc, M. Shayegan and D.A.
Huse, Phys. Rev. Lett. \textbf{93} (2004) 036802] at $\nu =1$. | 0701063v1 |
1995-12-08 | The Complex Structure of 2D Surfaces | The complex structure of a surface generated by the two-dimensional dynamical
triangulation(DT) is determined by measuring the resistivity of the surface. It
is found that surfaces coupled to matter fields have well-defined complex
structures for cases when the matter central charges are less than or equal to
one, while they become unstable beyond c=1. A natural conjecture that fine
planar random network of resistors behave as a continuous sheet of constant
resistivity is justified numerically for c<1. | 9512014v1 |
2006-08-07 | Random walk on the incipient infinite cluster for oriented percolation in high dimensions | We consider simple random walk on the incipient infinite cluster for the
spread-out model of oriented percolation on $Z^d \times Z_+$. In dimensions
$d>6$, we obtain bounds on exit times, transition probabilities, and the range
of the random walk, which establish that the spectral dimension of the
incipient infinite cluster is 4/3, and thereby prove a version of the
Alexander--Orbach conjecture in this setting. The proof divides into two parts.
One part establishes general estimates for simple random walk on an arbitrary
infinite random graph, given suitable bounds on volume and effective resistance
for the random graph. A second part then provides these bounds on volume and
effective resistance for the incipient infinite cluster in dimensions $d>6$, by
extending results about critical oriented percolation obtained previously via
the lace expansion. | 0608164v2 |
2003-02-21 | New results from an extensive aging test on bakelite Resistive Plate Chambers | We present recent results of an extensive aging test, performed at the CERN
Gamma Irradiation Facility on two single--gap RPC prototypes, developed for the
LHCb Muon System. With a method based on a model describing the behaviour of an
RPC under high particle flux conditions, we have periodically measured the
electrode resistance R of the two RPC prototypes over three years: we observe a
large spontaneous increase of R with time, from the initial value of about 2
MOhm to more than 250 MOhm. A corresponding degradation of the RPC rate
capabilities, from more than 3 kHz/cm2 to less than 0.15 kHz/cm2 is also found. | 0302077v2 |
2004-03-09 | Measuring the force ejecting DNA from phage | We discuss how a balance can be established between the force acting to eject
DNA from viral capsids and the force resisting its entry into a colloidal
suspension which mimics the host cell cytoplasm. The ejection force arises from
the energy stored in the capsid as a consequence of the viral genome
(double-stranded DNA) being strongly bent and crowded on itself. The resisting
force is associated with the osmotic pressure exerted by the colloidal
particles in the host solution. Indeed, recent experimental work has
demonstrated that the extent of ejection can be progressively limited by
increasing the external osmotic pressure; at a sufficiently high pressure the
ejection is completely suppressed. We outline here a theoritical analysis that
allows a determination of the internal (capsid) pressure by examining the
different relations between force and pressure inside and outside the capsid,
using the experimentally measured position of the force balance. | 0403057v1 |
2006-08-04 | Design guide for electronics for resistive charge division in thermal neutron detection | An amplifier has been designed for optimal use of position sensitive thermal
neutron detectors using the principle of resistive charge division. The
important points in this optimization are: high counting rates and good spatial
resolution. This amplifier is built as a hybrid circuit and is now used on
several new instruments at the ILL. It consists of a fast low noise current
pre-amplifier, a gaussian shaping circuit based on a 4th order active filter
and an essentially noiseless baseline reconstruction. In this paper, we present
a rather complete theoretical analysis of the problem that lead us to the
choices made above, and allows for an optimal adaptation to other situations.
An analysis of unwanted, secondary effects is also worked out. | 0608046v1 |
2002-05-20 | A Zoology of Bell inequalities resistant to detector inefficiency | We derive both numerically and analytically Bell inequalities and quantum
measurements that present enhanced resistance to detector inefficiency. In
particular we describe several Bell inequalities which appear to be optimal
with respect to inefficient detectors for small dimensionality d=2,3,4 and 2 or
more measurement settings at each side. We also generalize the family of Bell
inequalities described in Collins et all (Phys. Rev. Lett. 88, 040404) to take
into account the inefficiency of detectors. In addition we consider the
possibility for pairs of entangled particles to be produced with probability
less than one. We show that when the pair production probability is small, one
must in general use different Bell inequalities than when the pair production
probability is high. | 0205130v2 |
2007-05-17 | Incoherent non-Fermi liquid scattering in a Kondo lattice | One of the most notorious non-Fermi liquid properties of both archetypal
heavy-fermion systems [1-4] and the high-Tc copper oxide superconductors [5] is
an electrical resistivity that evolves linearly with temperature, T. In the
heavy-fermion superconductor CeCoIn5 [5], this linear behaviour was one of the
first indications of the presence of a zero-temperature instability, or quantum
critical point. Here, we report the observation of a unique control parameter
of T-linear scattering in CeCoIn5, found through systematic chemical
substitutions of both magnetic and non-magnetic rare-earth, R, ions into the Ce
sub-lattice. We find that the evolution of inelastic scattering in Ce1-xRxCoIn5
is strongly dependent on the f-electron configuration of the R ion, whereas two
other key properties -- Cooper-pair breaking and Kondo-lattice coherence -- are
not. Thus, T-linear resistivity in CeCoIn5 is intimately related to the nature
of incoherent scattering centers in the Kondo lattice, which provides insight
into the anomalous scattering rate synonymous with quantum criticality [7]. | 0705.2592v2 |
2007-07-22 | Investigations of a THGEM-based imaging detector | We present the results of our recent studies on a Thick Gas Electron
Multiplier (THGEM)-based imaging detector prototype. It consists of two 100x100
mm^2 THGEM electrodes in cascade, coupled to a resistive anode. The event
location is recorded with a 2D double-sided readout electrode equipped with
discrete delay-lines and dedicated electronics. The THGEM electrodes, produced
by standard printed-circuit board and mechanical drilling techniques, a 0.4 mm
thick with 0.5 mm diameter holes spaced by 1 mm. Localization resolutions of
about 0.7 mm (FWHM) were measured with soft x-rays, in a detector operated with
atmospheric-pressure Ar/CH4; good linearity and homogeneity were achieved. We
describe the imaging-detector layout, the resistive-anode 2D readout system and
the imaging properties. The THGEM has numerous potential applications that
require large-area imaging detectors, with high-rate capability,
single-electron sensitivity and moderate (sub-mm) localization resolution. | 0707.3257v3 |
2007-08-13 | Optimized minigaps for negative differential resistance creation in strongly delta-doped (1D) superlattices | The "atomic saw method" uses the passage of dislocations in two-dimensional
(2D) quantum-well superlattices to create periodic slipping layers and
one-dimensional (1D) quantum wire superlattices. The effects of this space
structuring of the samples on the allowed energies are analysed in the case of
GaAs d-doped superlattices. If they are sufficiently large, the various
minigaps appearing in the 1D band structure could be responsible for the
presence of negative differential resistance (NDR) with high critical current
in these systems. The purpose is to determine the evolution of the minigaps in
terms of the sample parameters and to obtain the means to determine both the 2D
and 1D structural characteristics where NDR could appear. | 0708.1673v1 |
2007-09-13 | Influence of Mg Deficiency on the Superconductivity in MgB2 Thin Films Grown by using HPCVD | The effects of Mg deficiency in MgB2 films grown by using hybrid
physical-chemical vapor deposition were investigated after vacuum annealing at
various temperatures. High-quality MgB2 films grown on c-cut Al2O3 substrates
with different superconducting transition temperatures (Tc) of 40.2 and 41 K
were used in this study. As the annealing temperature was increased from 200 to
800 C, the Mg contents in the MgB2 films systemically decreased, but the Tc's
did not change, within 0.12 K, until the annealing temperature reached 700 C.
For MgB2 films annealed at 800 C for 30 min, however, no superconductivity was
observed, and the temperature dependence of the resistivity showed a
semiconducting behavior. We also found that the residual resistivity ratio
decreased with increasing annealing temperature. | 0709.1989v1 |
2007-12-20 | The evolution of the Non-Fermi Liquid behavior of BaVS$_3$ under high pressure | Temperature, pressure, and magnetic field dependencies of the resistivity of
BaVS$_3$ were measured above the critical pressure of $p_{cr}$=2 GPa, which is
associated with the zero temperature insulator-to-metal (MI) transition. The
resistivity exhibits the $T^n$ temperature dependence below $T_g\approx$15 K,
with $n$ of 1.5 at $p_{cr}$, which increases continuously with pressure towards
2. This is interpreted as a crossover from non-Fermi (NFL) to Fermi-liquid (FL)
behavior. Although the spin configuration of the $e_g$ electrons influences the
charge propagation, the NFL behavior is attributed to the pseudogap that
appears in the single particle spectrum of the $d_z^2$ electrons related to
large quasi-one dimensional (Q-1d) 2$k_F$-CDW fluctuations. The non-monotonic
magnetic field dependence of $\Delta$$\rho$/$\rho$ reveals a characteristic
field $B_0\approx$12 T attributed to the full suppression of the pseudogap. | 0712.3393v1 |
2008-02-05 | Verwey transition in Fe$_{3}$O$_{4}$ at high pressure: quantum critical behavior at the onset of metallization | We provide evidence for the existence of a {\em quantum critical point} at
the metallization of magnetite Fe$_{3}$O$_{4}$ at an applied pressure of $p_{c}
\approx 8$ GPa. We show that the present ac magnetic susceptibility data
support earlier resistivity data. The Verwey temperature scales with pressure
$T_{V}\sim (1-p/p_{c})^{\nu}$, with $\nu\sim 1/3$. The resistivity data shows a
temperature dependence $\rho(T)=\rho_{0}+AT^{n}$, with $n\simeq 3$ above and
2.5 at the critical pressure, respectively. This difference in $n$ with
pressure is a sign of critical behavior at $p_{c}$. The magnetic susceptibility
is smooth near the critical pressure, both at the Verwey transition and near
the ferroelectric anomaly. A comparison with the critical behavior observed in
the Mott-Hubbard and related systems is made. | 0802.0631v1 |
2008-02-20 | Development of bakelite based Resistive Plate Chambers | A Comparative study has been performed on Resistive Plate Chambers made of
different grades of bakelite paper laminates, produced and commercially
available in India. The chambers, operated in the streamer mode using argon :
tetrafluroethane : isobutane in 34:59:7 mixing ratio, are tested with cosmic
rays for the efficiency and the stability with cosmic rays. A particular grade
of bakelite (P-120, NEMA LI-1989 Grade XXX), used for high voltage insulation
in humid conditions, was found to give satisfactory performance with stable
efficiency of > 96% continuously for more than 110 days. A silicone treatment
of the inner surfaces of the bakelite RPC is found to be necessary for
operation of the detector. | 0802.2766v1 |
2008-03-06 | Graph Sparsification by Effective Resistances | We present a nearly-linear time algorithm that produces high-quality
sparsifiers of weighted graphs. Given as input a weighted graph $G=(V,E,w)$ and
a parameter $\epsilon>0$, we produce a weighted subgraph
$H=(V,\tilde{E},\tilde{w})$ of $G$ such that $|\tilde{E}|=O(n\log
n/\epsilon^2)$ and for all vectors $x\in\R^V$ $(1-\epsilon)\sum_{uv\in
E}(x(u)-x(v))^2w_{uv}\le \sum_{uv\in\tilde{E}}(x(u)-x(v))^2\tilde{w}_{uv} \le
(1+\epsilon)\sum_{uv\in E}(x(u)-x(v))^2w_{uv}. (*)$
This improves upon the sparsifiers constructed by Spielman and Teng, which
had $O(n\log^c n)$ edges for some large constant $c$, and upon those of
Bencz\'ur and Karger, which only satisfied (*) for $x\in\{0,1\}^V$.
A key ingredient in our algorithm is a subroutine of independent interest: a
nearly-linear time algorithm that builds a data structure from which we can
query the approximate effective resistance between any two vertices in a graph
in $O(\log n)$ time. | 0803.0929v4 |
2008-03-12 | Bardeen-Stephen flux flow law disobeyed in the high-$T_c$ superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ | Pulsed high current experiments in single crystals of the high-$T_{c}$
superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ in c-axis directed
magnetic field $H$ reveal that the $ab$-face resistance in the free flux flow
regime is a solely logarithmic function of H, devoid of any power law
component. Re-analysis of published data confirms this result and leads to
empirical analytic forms for the $ab$-plane and c-axis resistivities:
$\rho_{ab}\propto$ $H^{3/4}$, which does not obey the expected Bardeen-Stephen
result for free flux flow, and $\rho_{c} \propto H^{-3/4} \log^{2}H$. | 0803.1804v1 |
2008-05-05 | Fast dynamos in weakly ionized gases | The turnover of interstellar gas on $\sim 10^9$yr timescales argues for the
continuous operation of a galactic dynamo. The conductivity of interstellar gas
is so high that the dynamo must be "fast" - i.e. the magnetic field must be
amplified at a rate nearly independent of the magnetic diffusivity. Yet, all
the fast dynamos so far known - and all direct numerical simulations of
interstellar dynamos - yield magnetic power spectra that peak at the resistive
scale, while galactic magnetic fields have substantial power on large scales.
In this paper we show that in weakly ionized gas the limiting scale may be the
ion-neutral decoupling scale, which although still small is many orders of
magnitude larger than the resistive scale. | 0805.0412v1 |
2008-05-26 | Negative differential resistance in molecular junctions: application to graphene ribbon junctions | Using self-consistent calculations based on Non-Equilibrium Green's Function
(NEGF) formalism, the origin of negative differential resistance (NDR) in
molecular junctions and quantum wires is investigated. Coupling of the molecule
to electrodes becomes asymmetric at high bias due to asymmetry between its
highest occupied molecular orbital (HOMO) and lowest unoccupied molecular
orbital (LUMO) levels. This causes appearance of an asymmetric potential
profile due to a depletion of charge and reduction of screening near the source
electrode. With increasing bias, this sharp potential drop leads to an enhanced
localization of the HOMO and LUMO states in different parts of the system. The
reduction in overlap, caused by localization, results in a significant
reduction in the transmission coefficient and current with increasing bias. An
atomic chain connected to two Graphene ribbons was investigated to illustrate
these effects. For a chain substituting a molecule, an even-odd effect is also
observed in the NDR characteristics. | 0805.3980v1 |
2008-06-10 | Are Microwave Induced Zero Resistance States Necessarily Static? | We study the effect of inhomogeneities in Hall conductivity on the nature of
the Zero Resistance States seen in the microwave irradiated two-dimensional
electron systems in weak perpendicular magnetic fields, and we show that
time-dependent domain patterns may emerge in some situations. For an annular
Corbino geometry, with an equilibrium charge density that varies linearly with
radius, we find a time-periodic non-equilibrium solution, which might be
detected by a charge sensor, such as an SET. For a model on a torus, in
addition to static domain patterns seen at high and low values of the
equilibrium charge inhomogeneity, we find that, in the intermediate regime, a
variety of nonstationary states can also exist. We catalog the possibilities we
have seen in our simulations. Within a particular phenomenological model, we
show that linearizing the nonlinear charge continuity equation about a
particularly simple domain wall configuration and analyzing the eigenmodes
allows us to estimate the periods of the solutions to the full nonlinear
equation. | 0806.1562v1 |
2008-06-13 | Synthesis, crystal structure, microstructure, transport and magnetic properties of SmFeAsO and SmFeAs(O0.93F0.07) | SmFeAsO and the isostructural superconducting SmFeAs(O0.93F0.07) samples were
prepared. Characterization by means of Rietveld refinement of X-ray powder
diffraction data, scanning electron microscope observation, transmission
electron microscope analysis, resistivity and magnetization measurements were
carried out. Sintering treatment strongly improves the grain connectivity, but,
on the other hand, induces a competition between the thermodynamic stability of
the oxy-pnictide and Sm2O3, hence worsening the purity of the sample. In the
pristine sample both magnetization and resistivity measurements clearly
indicate that two different sources of magnetism are present: the former
related to Fe ordering at 140 K and the latter due to the Sm ions that orders
antiferromagnetically at low temperature. The feature at 140 K disappears in
the F-substituted sample and, at low temperatures a superconducting transition
appears. The magnetoresistivity curves of the F-substituted sample probably
indicates very high critical field values. | 0806.2205v1 |
2008-07-17 | Photosensitive Strip RETHGEM | An innovative photosensitive gaseous detector, consisting of a GEM like
amplification structure with double layered electrodes (instead of commonly
used metallic ones) coated with a CsI reflective photocathode, is described. In
one of our latest designs, the inner electrode consists of a metallic grid and
the outer one is made of resistive strips; the latter are manufactured by a
screen printing technology on the top of the metallic strips grid The inner
metallic grid is used for 2D position measurements whereas the resistive layer
provides an efficient spark protected operation at high gains - close to the
breakdown limit. Detectors with active areas of 10cm x10cm and 10cm x20cm were
tested under various conditions including the operation in photosensitive gas
mixtures containing ethylferrocene or TMAE vapors. The new technique could have
many applications requiring robust and reliable large area detectors for UV
visualization, as for example, in Cherenkov imaging devices. | 0807.2718v1 |
2008-07-21 | Superconductivity at 34.7 K in the iron arsenide Eu0.7Na0.3Fe2As2 | EuFe2As2 is a member of the ternary iron arsenide family. Similar to BaFe2As2
and SrFe2As2, EuFe2As2 exhibits a clear anomaly in resistivity near 200 K. It
suggests that EuFe2As2 is another promising parent compound in which
superconductivity may be realized by appropriate doping. Here we report the
discovery of superconductivity in Eu0.7Na0.3Fe2As2 by partial substitution of
the europium site with sodium. ThCr2Si2 tetragonal structure, as expected for
EuFe2As2, is formed as the main phase for the composition Eu0.7Na0.3Fe2As2.
Resistivity measurement reveals a transition temperature as high as 34.7 K in
this compound, which is higher than the Tc of Eu0.5K0.5Fe2As2. | 0807.3293v3 |
2008-08-03 | Magnetic and Transport Studies on Electron-doped CeFeAsO1-xFx Superconductor | The magnetic and transport behaviors of cerium substituted iron oxy-arsenide
superconductor with x = 0.1 to 0.4 fluoride (F) doping have been investigated
in this report. Temperature dependent susceptibility and resistivity
measurements showed the 0.1 F-doped sample (CeFeAsO0.9F0.1) has a
superconducting transition temperature (Tc) of around 30 K. With increasing
doping beyond x = 0.2 Tc saturates to around 40 K. Temperature dependent
susceptibility measured in different magnetic fields for the under-doped sample
showed Meissner effect in low field and the diamagnetism is still visible up to
1 Tesla, with an obvious magnetic transition below 5 K, perhaps originating
from magnetic ordering of the rare earth cerium. The corresponding field
dependent resistance versus temperature measurements indicated a broadening of
less than 3 K for Tc at mid-point by increasing the field to 5 Tesla indicating
rather low anisotropy. An estimated upper critical field of more than 48 Tesla
and accordingly an estimated maximum coherence length of 2.6 nm were obtained
confirming the high upper critical field with a short coherence length for this
superconductor. | 0808.0296v1 |
2008-08-22 | Correlation between extrinsic electroresistance and magnetoresistance in fine-grained La0.7Ca0.3MnO3 | We report our observation of a correlation between the extrinsic
electroresistance (EER) and magnetoresistance (EMR) via grain size in
fine-grained La0.7Ca0.3MnO3. The nature of dependence of EER and EMR on grain
size (~0.2-1.0 micron) indicates that for finer grains with low-resistive
boundaries both of them follow similar trend whereas they differ for coarser
grains with high-resistive boundaries. This could be due to a crossover in the
mechanism of charge transport across the grain boundaries - from spin-depedent
scattering process to spin-polarized tunneling one - as a function of grain
size. | 0808.3043v2 |
2008-09-28 | Scaling of 1/f noise in tunable break-junctions | We have studied the $1/f$ voltage noise of gold nano-contacts in
electromigrated and mechanically controlled break-junctions having resistance
values $R$ that can be tuned from 10 $\Omega$ (many channels) to 10 k$\Omega$
(single atom contact). The noise is caused by resistance fluctuations as
evidenced by the $S_V\propto V^2$ dependence of the power spectral density
$S_V$ on the applied DC voltage $V$. As a function of $R$ the normalized noise
$S_V/V^2$ shows a pronounced cross-over from $\propto R^3$ for low-ohmic
junctions to $\propto R^{1.5}$ for high-ohmic ones. The measured powers of 3
and 1.5 are in agreement with $1/f$-noise generated in the bulk and reflect the
transition from diffusive to ballistic transport. | 0809.4841v1 |
2008-10-20 | Polaron relaxation and hopping conductivity in LaMn$_{1-x}$Fe$_{x}$O$_3$ | Dc and ac transport properties as well as electric modulus spectra have been
investigated for the samples LaMn$_{1-x}$Fe$_{x}$O$_3$ with compositions 0
$\leq x \leq$ 1.0. The bulk dc resistivity shows a temperature variation
consistent with the variable range hopping mechanism at low temperature and
Arrhenius mechanism at high temperatures. The ac conductivity has been found to
follow a power law behavior at a limited temperature and frequency region where
Anderson-localization plays a significant role in the transport mechanism for
all the compositions. At low temperatures large dc resistivities and dielectric
relaxation behavior for all the compositions are consistent with the polaronic
nature of the charge carriers. Scaling of the modulus spectra shows that the
charge transport dynamics is independent of temperature for a particular
composition but depends strongly on different compositions possibly due to
different charge carrier concentrations and structural properties. | 0810.3502v1 |
2008-11-05 | Superconductivity at 56 K in Samarium-doped SrFeAsF | We synthesized the samples Sr$_{1-x}$Sm$_x$FFeAs with ZrCuSiAs-type
structure. These samples were characterized by resistivity and susceptibility.
It is found that substitution of rare earth metal for alkaline earth metal in
this system suppresses the anomaly in resistivity and induces
superconductivity. Superconductivity at 56 K in nominal composition
Sr$_{0.5}$Sm$_{0.5}$FFeAs is realized, indicating that the superconducting
transition temperatures in the iron arsenide fluorides can reach as high as
that in oxypnictides with the same structure. | 0811.0761v3 |
2008-12-31 | Cosmic-ray driven dynamo in galactic disks | We present new developments on the Cosmic--Ray driven, galactic dynamo,
modeled by means of direct, resistive CR--MHD simulations, performed with ZEUS
and PIERNIK codes. The dynamo action, leading to the amplification of
large--scale galactic magnetic fields on galactic rotation timescales, appears
as a result of galactic differential rotation, buoyancy of the cosmic ray
component and resistive dissipation of small--scale turbulent magnetic fields.
Our new results include demonstration of the global--galactic dynamo action
driven by Cosmic Rays supplied in supernova remnants. An essential outcome of
the new series of global galactic dynamo models is the equipartition of the gas
turbulent energy with magnetic field energy and cosmic ray energy, in saturated
states of the dynamo on large galactic scales. | 0901.0111v1 |
2009-01-13 | Spin-Orbit Scattering and Quantum Metallicity in Ultra-Thin Be Films | We compare and contrast the low temperature magnetotransport properties of
ultra-thin, insulating, Be films with and without spin-orbit scattering (SOS).
Beryllium films have very little intrinsic SOS, but by "dusting" them with
sub-monolayer coverages of Au, one can introduce a well controlled SOS rate.
Pure Be films with sheet resistance R >R_Q exhibit a low-temperature negative
magnetoresistance (MR) that saturates to the quantum resistance R_Q = h/e^2.
This high-field quantum metal phase is believed to represent a new ground state
of the system. In contrast, the corresponding negative MR in Be/Au films is
greatly diminished, suggesting that, in the presence of strong SOS, the quantum
metal phase can only be reached at field scales well beyond those typically
available in a low temperature laboratory. | 0901.1873v1 |
2009-02-12 | Two-Fluid Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection | We investigate the large scale evolution of a relativistic magnetic
reconnection in an electron-positron pair plasma by a relativistic two-fluid
magnetohydrodynamic (MHD) code. We introduce an inter-species friction force as
an effective resistivity to dissipate magnetic fields. We demonstrate that
magnetic reconnection successfully occurs in our two-fluid system, and that it
involves Petschek-type bifurcated current layers in later stage. We further
observe a quasi-steady evolution thanks to an open boundary condition, and find
that the Petschek-type structure is stable over the long time period.
Simulation results and theoretical analyses exhibit that the Petschek outflow
channel becomes narrower when the reconnection inflow contains more magnetic
energy, as previously claimed. Meanwhile, we find that the reconnection rate
goes up to ~1 in extreme cases, which is faster than previously thought. The
role of the resistivity, implications for reconnection models in the
magnetically dominated limit, and relevance to kinetic reconnection works are
discussed. | 0902.2074v2 |
2009-03-03 | Insulating Phases Induced by Crossing of Partially Filled Landau Levels in a Si Quantum Well | We study magnetotransport in a high mobility Si two-dimensional electron
system by in situ tilting of the sample relative to the magnetic field. A
pronounced dip in the longitudinal resistivity is observed during the Landau
level crossing process for noninteger filling factors. Together with a Hall
resistivity change which exhibits the particle-hole symmetry, this indicates
that electrons or holes in the relevant Landau levels become localized at the
coincidence where the pseudospin-unpolarized state is expected to be stable. | 0903.0486v2 |
2009-03-22 | The Turbulent Magnetic Prandtl Number of MHD Turbulence in Disks | The magnetic Prandtl number Pr_M is the ratio of viscosity to resistivity. In
astrophysical disks the diffusion of angular momentum (viscosity) and magnetic
fields (resistivity) are controlled by turbulence. Phenomenological models of
the evolution of large scale poloidal magnetic fields in disks suggest that the
turbulent magnetic Prandtl number Pr_{M,T} controls the rate of escape of
vertical field from the disk; for Pr_{M,T} leq R/H vertical field diffuses
outward before it can be advected inward by accretion. Here we measure field
diffusion and angular momentum transport due to MHD turbulence in a shearing
box, and thus Pr_{M,T}, by studying the evolution of a sinusoidal perturbation
in the magnetic field that is injected into a turbulent background. We show
that the perturbation is always stable, decays approximately exponentially, has
decay rate proportional to k^2, and that the implied Pr_{M,T} ~ 1. | 0903.3757v1 |
2009-04-08 | Gate-controlled non-volatile graphene-ferroelectric memory | In this letter, we demonstrate a non-volatile memory device in a graphene FET
structure using ferroelectric gating. The binary information, i.e. "1" and "0",
is represented by the high and low resistance states of the graphene working
channels and is switched by controlling the polarization of the ferroelectric
thin film using gate voltage sweep. A non-volatile resistance change exceeding
200% is achieved in our graphene-ferroelectric hybrid devices. The experimental
observations are explained by the electrostatic doping of graphene by electric
dipoles at the ferroelectric/graphene interface. | 0904.1326v2 |
2009-04-13 | Breakdown of the N=0 Quantum Hall State in graphene: two insulating regimes | We studied the unusual Quantum Hall Effect (QHE) near the charge neutrality
point (CNP) in high-mobility graphene sample for magnetic fields up to 18 T. We
observe breakdown of the delocalized QHE transport and strong increase in
resistivities $\rho_{xx},|\rho_{xy}|$ with decreasing Landau level filling for
$\nu < 2$, where we identify two insulating regimes. For $1 \gtrsim |\nu|
\gtrsim 1/2$ we find an exponential increase of $\rho_{xx,xy} \sim
e^{a(H-H_c)}$ within the range up to several resistance quanta $R_K$, while the
Hall effect gradually disappears, consistent with the Hall insulator (HI) with
local transport. Then, at $\nu \approx 1/2$ a cusp in $\rho_{xx}(H)$ followed
by an onset of even faster growth indicates transition to a collective
insulator (CI) state. The likely candidate for this state is a pinned Wigner
crystal. | 0904.1996v3 |
2009-08-03 | The role of thermal conduction in magnetized viscous-resistive ADAFs | Observations of the hot gas, which is surrounding Sgr A* and a few other
nearby galactic nuclei, imply that mean free paths of electron and proton are
comparable to gas capture radius. So, hot accretion flows likely proceed under
week collision conditions. As a result thermal conduction by ions has a
considerable contribution in transfer of the realized heat in accretion
mechanisms. We study a 2D advective accretion disk bathed in a poloidal
magnetic field of a central accretor in the presence of thermal conduction. We
find self-similar solutions for an axisymmetric, rotating, steady,
viscose-resistive, magnetized accretion flow. The dominant mechanism of energy
dissipation is assumed to be turbulence viscosity and magnetic diffusivity due
to magnetic field of the central accretor. We show that the global structure of
ADAFs are sensitive to viscosity, advection and thermal conduction parameters.
We discuss how radial flow, angular velocity and density of accretion flows may
vary with the advection, thermal conduction and viscous parameters. | 0908.0325v1 |
2009-08-23 | Direct Measurement of Thermal Fluctuation of High-Q Pendulum | We achieved for the first time a direct measurement of the thermal
fluctuation of a pendulum in an off-resonant region using a laser
interferometric gravitational wave detector. These measurements have been well
identified for over one decade by an agreement with a theoretical prediction,
which was derived by a fluctuation-dissipation theorem. Thermal fluctuation is
dominated by the contribution of resistances in coil-magnet actuator circuits.
When we tuned these resistances, the noise spectrum also changed according to a
theoretical prediction. The measured thermal noise level corresponds to a high
quality factor on the order of 10^5 of the pendulum. | 0908.3227v1 |
2009-08-25 | Superconductivity in a single C60 transistor | Single molecule transistors (SMTs) are currently attracting enormous
attention as possible quantum information processing devices. An intrinsic
limitation to the prospects of these however is associated to the presence of a
small number of quantized conductance channels, each channel having a high
access resistance of at best $R_{K}/2=h/2e^{2}$=12.9 k$\Omega$. When the
contacting leads become superconducting, these correlations can extend
throughout the whole system by the proximity effect. This not only lifts the
resistive limitation of normal state contacts, but further paves a new way to
probe electron transport through a single molecule. In this work, we
demonstrate the realization of superconducting SMTs involving a single C60
fullerene molecule. The last few years have seen gate-controlled Josephson
supercurrents induced in the family of low dimensional carbon structures such
as flakes of two-dimensional graphene and portions of one-dimensional carbon
nanotubes. The present study involving a full zero-dimensionnal fullerene
completes the picture. | 0908.3638v1 |
2009-08-26 | Observation of quantum-Hall effect in gated epitaxial graphene grown on SiC (0001) | Epitaxial graphene films were formed on the Si-face of semi-insulating 4H-SiC
substrates by a high temperature sublimation process. A high-k gate stack on
epitaxial graphene is realized by inserting a fully oxidized nanometer thin
aluminum film as a seeding layer followed by an atomic-layer deposition
process. The electrical properties of epitaxial graphene films are sustained
after gate stack formation without significant degradation. At low
temperatures, the quantum-Hall effect in Hall resistance is observed along with
pronounced Shubnikov-de Hass oscillations in diagonal magneto-resistance of
gated epitaxial graphene on SiC (0001). | 0908.3822v3 |
2009-12-03 | C-axis critical current of a PrFeAsO0.7 single crystal | The c-axis transport properties of a high-pressure synthesized PrFeAsO0.7
single crystal are studied using s-shaped junctions. Resistivity anisotropy of
about 120 detected at 50 K shows the presence of strong anisotropy in the
electronic states. The obtained critical current density for the c-axis of
2.9*10^5 A/cm^2 is two orders of magnitude larger than that in
Bi2Sr1.6La0.4CuO6+d. The appearance of a hysteresis in the current-voltage
curve below T_c is the manifestation of the intrinsic Josephson effect similar
to that in cuprate superconductors. The suppression of the critical
current-normal resistance (I_cR_n) product is explained by an inspecular
transport in s_pm-wave pair potential. | 0912.0598v1 |
2010-01-12 | Resistive Magnetic Field Generation at Cosmic Dawn | Relativistic charged particles (CR for cosmic-rays) produced by Supernova
explosion of the first generation of massive stars that are responsible for the
re-ionization of the universe escape into the intergalactic medium, carrying an
electric current. Charge imbalance and induction give rise to a return current,
$\vec j_t$, carried by the cold thermal plasma which tends to cancel the CR
current. The electric field, $\vec E=\eta \vec j_t$, required to draw the
collisional return current opposes the outflow of low energy cosmic rays and
ohmically heats the cold plasma. Owing to inhomogeneities in the resistivity,
$\eta(T)$, caused by structure in the temperature, $T$, of the intergalactic
plasma, the electric field possesses a rotational component which sustains
Faraday's induction. It is found that magnetic field is robustly generated
throughout intergalactic space at rate of 10$^{-17}-10^{-16}$ Gauss/Gyr, until
the temperature of the intergalactic medium is raised by cosmic reionization.
The magnetic field may seed the subsequent growth of magnetic fields in the
intergalactic environment. | 1001.2011v2 |
2010-01-19 | Theory of Normal State Pseudogap Behavior in FeSe(1-x)$Te(x) | The normal state of the recently discovered Iron Selenide (FeSe)-based
superconductors shows a range of inexplicable features. Along with bad-metallic
resistivity, characteristic pseudogap features and proximity to insulating
states, reminiscent of the underdoped high-Tc cuprates, mark these systems as
strongly correlated non-Fermi Liquid metals. Here, using the first-principles
LDA+DMFT method, we show how strong multi-orbital correlation-induced
orbital-selective Mott-like physics leads to an orthogonality catastrophe
underpinning these inexplicable incoherent features. Excellent agreement with a
range of resistivity and Seebeck data strongly support our proposal. We discuss
pseudogap regime microscopically, along with implications for the nature of the
instability at lower T, and propose that related systems could be of use in
thermoelectric devices. | 1001.3273v1 |
2010-02-08 | Indirect Magnetic-Field-Tuned Superconductor-Insulator Transitions and Weak Localization of Bosons of Quasi-Two Dimensional Metal Films | Magnetic field and electrostatically tuned superconductor-insulator (SI)
transitions of ultrathin metal films with levels of disorder that place them
near the disorder-tuned SI transition appear to be direct, continuous quantum
phase transitions. When films with lower levels of disorder are subjected to a
perpendicular magnetic field, instead of a direct transition, a mixed
superconductor-nonsuperconductor regime emerges at the lowest temperatures. The
zero temperature limit of the resistance is either insulating or
superconducting, depending upon the value of the field, suggesting that the
behavior in this limit is governed by percolation physics. At high fields and
low temperatures, in the nominally insulating regime, the resistance rather
than the conductance is found to be a logarithmic function of temperature
corresponding to predicitons for the weak localization of bosons. | 1002.1720v1 |
2010-02-16 | Dynamic Nuclear Polarization and Nuclear Magnetic Resonance in the Simplest Pseudospin Quantum Hall Ferromagnet | We present dynamic nuclear polarization (DNP) in the simplest pseudospin
quantum Hall ferromagnet (QHF) of an InSb two-dimensional electron gas with a
large g factor using tilted magnetic fields. The DNP-induced amplitude change
of a resistance spike of the QHF at large current enables observation of the
resistively detected nuclear magnetic resonance of the high nuclear spin
isotope 115In with nine quadrupole splittings. Our results demonstrate the
importance of domain structures in the DNP process. The nuclear spin relaxation
time T1 in this QHF was relatively short (~ 120 s), and almost temperature
independent. | 1002.3087v3 |
2010-02-28 | Microwave-induced magnetoresistance of two-dimensional electrons interacting with acoustic phonons | The influence of electron-phonon interaction on magnetotransport in
two-dimensional electron systems under microwave irradiation is studied
theoretically. Apart from the phonon-induced resistance oscillations which
exist in the absence of microwaves, the magnetoresistance of irradiated samples
contains oscillating contributions due to electron scattering on both
impurities and acoustic phonons. The contributions due to electron-phonon
scattering are described as a result of the interference of phonon-induced and
microwave-induced resistance oscillations. In addition, microwave heating of
electrons leads to a special kind of phonon-induced oscillations. The relative
strength of different contributions and their dependence on parameters are
discussed. The interplay of numerous oscillating contributions suggests a
peculiar magnetoresistance picture in high-mobility layers at the temperatures
when electron-phonon scattering becomes important. | 1003.0178v1 |
2010-03-19 | Evidence for Anisotropic Vortex Dynamics and Pauli Limitation in the Upper Critical Field of FeSe1-xTex | We have determined HC2(T) for FeSe1-xTex (x=0.52) single crystals using
resistivity measurements at high static and pulsed magnetic field, as well as
specific heat measurements up to 9T. We find that the significant anisotropy of
the initial slope of HC2(T) determined from resistivity measurements, is not
present when HC2 is determined from the specific heat results. This suggests
that the thermodynamic upper critical field is almost isotropic, and that
anisotropic vortex dynamics play a role. Further evidence of anisotropic vortex
dynamics is found in the behaviour in pulsed field. We also find that Pauli
limiting must be included in order to fit the temperature dependence of HC2,
indicating probably higher effective mass in FeSe1-xTex than in other Fe
superconductors. | 1003.3812v1 |
2010-03-29 | Three Dimensional Superconductivity in FeSe with Tczero Up to 10.9 K Induced by Internal Strain | Polycrystalline sample FeSe was synthesized by a self-flux solution method
which shows a zero resistance temperature up to 10.9 K and a Tconset (90%
\rhon, \rhon: normal state resistivity) up to 13.3 K. The decrease of
superconducting transition temperature by heat treatment indicates that
internal crystallographic strain which plays the same effect as external
pressure is the origin of its high Tc. The fluctuation conductivity was studied
which could be well described by 3D Aslamazov-Larkin (AL) power law. The
estimated value of coherence length \xic=9.2 \AA is larger than the distance
between conducting layers (~6.0 \AA), indicating the three-dimensional nature
of superconductivity in this compound. | 1003.5415v1 |
2010-06-01 | Synthesis, structural and physical properties of $δ'$-FeSe$_{1-x}$ | We report on synthesis, structural characterization, resistivity, magnetic
and thermal expansion measurements on the as yet unexplored $\delta'$-phase of
FeSe$_{1-x}$, here synthesized under ambient- (AP) and high-pressure (HP)
conditions. We show that in contrast to $\beta$-FeSe$_{1-x}$, monophasic
superconducting $\delta'$-FeSe$_{1-x}$ can be obtained in off-stoichiometric
samples with excess Fe atoms preferentially residing in the van der Waals gap
between the FeSe layers. The AP $\delta'$-FeSe$_{1-x}$ sample studied here
($T_c$ $\simeq$ 8.5\,K) possesses an unprecedented residual resistivity ratio
RRR $\simeq$ 16. Thermal expansion data reveal a small feature around
$\sim$90\,K, which resembles the anomaly observed at the structural and
magnetic transitions for other Fe-based superconductors, suggesting that some
kind of "magnetic state" is formed also in FeSe. %indicative of a fluctuating
magnetic ordering. For HP samples (RRR $\simeq$ 3), the disorder within the
FeSe layers is enhanced through the introduction of vacancies, the saturated
magnetic moment of Fe is reduced and only spurious superconductivity is
observed. | 1006.0073v2 |
2010-07-23 | Phonon-induced resistance oscillations of two-dimensional electron systems drifting with supersonic velocities | We present a theory of the phonon-assisted nonlinear dc transport of 2D
electrons in high Landau levels. The nonlinear dissipative resistivity displays
quantum magneto-oscillations governed by two parameters which are proportional
to the Hall drift velocity $v_H$ of electrons in electric field and the speed
of sound $s$. In the subsonic regime, $v_H<s$, the theory quantitatively
reproduces the oscillation pattern observed in recent experiments. We also find
the $\pi/2$ phase change of oscillations across the sound barrier $v_H=s$. In
the supersonic regime, $v_H>s$, the amplitude of oscillations saturates with
lowering temperature, while the subsonic region displays exponential
suppression of the phonon-assisted oscillations with temperature. | 1007.4211v1 |
2010-07-26 | Quantum phase transition of dynamical resistance in a mesoscopic capacitor | We study theoretically dynamic response of a mesoscopic capacitor, which
consists of a quantum dot connected to an electron reservoir via a point
contact and capacitively coupled to a gate voltage. A quantum Hall edge state
with a filling factor nu is realized in a strong magnetic field applied
perpendicular to the two-dimensional electron gas. We discuss a noise-driven
quantum phase transition of the transport property of the edge state by taking
into account an ohmic bath connected to the gate voltage. Without the noise,
the charge relaxation for nu>1/2 is universally quantized at R_q=h/(2e^2),
while for nu<1/2, the system undergoes the Kosterlitz-Thouless transtion, which
drastically changes the nature of the dynamical resistance. The phase
transition is facilitated by the noisy gate voltage, and we see that it can
occur even for an integer quantum Hall edge at nu=1. When the dissipation by
the noise is sufficiently small, the quantized value of R_q is shifted by the
bath impedance. | 1007.4404v1 |
2010-08-12 | Single crystal growth and superconducting properties of LiFeAs | We report the successful growth of high quality single crystals of LiFeAs
with lateral sizes up to 5 x 5 mm2 by the Sn-flux method. Electrical
resistivity studies reveal that the superconducting onset temperature is 18.2 K
with a transition width less than 1.1 K and the ratio of room temperature to
residual resistivity is about 24. Bulk superconductivity is supported by
perfect shielding in the magnetic susceptibility and a clear jump in the
specific heat Cp, resulting in deltaCp/T ~ 20.0 mJ/mol*K2. Upper critical field
slopes of dHc2c/dT ~ -1.39 and dHc2ab/dT ~ -2.99 T/K near Tc predict zero
temperature upper critical fields of Hc2c(0) ~ 17.2 and Hc2ab(0) ~ 36.9 T and
coherence lengths of Xi_ab = 4.4 and Xi_c = 2.0 nm in a single band model. This
result points to a modest superconducting anisotropy about 2.3 in LiFeAs. | 1008.2050v1 |
2010-09-07 | Mesoscopic transport in ultrathin films of La$_{0.67}$Ca$_{0.33}$MnO$_3$ | We investigate the electrical transport in mesoscopic structures of
La$_{0.67}$Ca$_{0.33}$MnO$_3$ in the regime of the metal-insulator transition
by fabricating microbridges from strained and unstrained thin films. We measure
current-voltage characteristics as function of temperature and in high magnetic
fields and with varying film thickness. For strained films, in warming from the
metallic to the insulating state, we find non-linear effects in the steep part
of the transition characterized by a differential resistance with a strong peak
around zero applied current, and saturating at higher currents after resistance
drops up to 60 %. We propose that this nonlinear behavior is associated with
melting of the insulating state by injecting charge carriers, signalling the
occurrence of an intervening phase which involves the formation of short range
polaron correlations. | 1009.1386v1 |
2010-09-28 | Influence of disorder on conductance in bilayer graphene under perpendicular electric field | Electron transport in bilayer graphene placed under a perpendicular electric
field is revealed experimentally. Steep increase of the resistance is observed
under high electric field; however, the resistance does not diverge even at low
temperatures. The observed temperature dependence of the conductance consists
of two contributions: the thermally activated (TA) conduction and the variable
range hopping (VRH) conduction. We find that for the measured electric field
range (0 - 1.3 V/nm) the mobility gap extracted from the TA behavior agrees
well with the theoretical prediction for the band gap opening in bilayer
graphene, although the VRH conduction deteriorates the insulating state more
seriously in bilayer graphene with smaller mobility. These results show that
the improvement of the mobility is crucial for the successful operation of the
bilayer graphene field effect transistor. | 1009.5467v1 |
2010-11-18 | Vortex density waves and negative absolute resistance in patterned superconductors | We study theoretically dynamical phases of vortices in superconducting films
with arrays of obstacles. By performing a series of molecular dynamics
simulations and analytical calculations, we demonstrate the existence of a
phase of soliton-like vortex-density waves appearing in a wide range of
parameters. These waves are formed by a self-assembled phase separation process
induced by strongly nonlinear density fluctuations of the moving vortex matter
above a certain critical driving current. At high vortex concentrations, the
waves move at an approximately current-independent speed resulting in a wide
plateau in the voltage-current characteristics. At stronger drives, the vortex
system enters into a fully jammed (zero-voltage) phase. By combining ac and dc
drives, the interplay between the vortex-density-wave and jammed phases leads
to the observation of negative absolute mobility of vortices, which induces the
superconducting film into a negative resistance state. | 1011.4172v2 |
2010-12-03 | Magnetic and electrical properties and carrier doping effects on the Fe-based host compound Sr4Sc2Fe2As2O6 | Additional charge carriers were introduced to the iron oxyarsenide
Sr4Sc2Fe2As2O6 under a high-pressure condition, followed by measurements of
electrical resistivity, Hall coefficient, and magnetic susceptibility. The host
compound Sr4Sc2Fe2As2O6 shows metallic conductivity down to ~200 K and turns to
show a semiconducting-like conductivity accompanied by a positive
magneto-resistance (22% at 70 kOe). Although the carrier density is comparable
at 300 K (5.9x1021 cm-3) with that of the other Fe-based superconductors, no
superconductivity appears down to 2 K. This is primarily because the net
carrier density decreases over 3 orders of magnitude on cooling and
additionally a possible magnetic order at ~120 K prevents carriers from
pairing. The properties were altered largely by introducing the additional
carriers. | 1012.0616v1 |
2010-12-06 | An analytical model of fractional overshooting | We predict resistance anomalies to be observed at high mobility two
dimensional electron systems (2DESs) in the fractional quantized Hall regime,
where the narrow (L <10 ?m) Hall bar is defined by top gates. An analytic
calculation scheme is used to describe the formation of integral and fractional
incompressible strips. We incorporate the screening properties of the 2DES,
together with the effects of perpendicular magnetic field, to calculate the
effective widths of the current carrying channels. The many-body effects are
included to our calculation scheme through the energy gap obtained from the
well accepted formulation of the composite fermions. We show that, the
fractional incompressible strips at the edges, assuming different filling
factors, become evanescent and co-exist at certain magnetic field intervals
yielding an overshoot at the Hall resistance. Similar to that of the integral
quantized Hall effect. We also provide a mechanism to explain the absence of
1/3 state at the Fabry-Perot interference experiments. Yet, an un-investigated
sample design is proposed to observe and enhance the fragile effects like
interference and overshooting based on our analytical model. | 1012.1294v1 |
2010-12-31 | Beam test of signal cross-talk and transmission for LMPRC | A new prototype of large area Multi-gap Resistive Plate Chamber (MRPC) with
long readout strips was built. This Long-strip Multi-gap Resistive Plate
Chamber (LMRPC) is double stacked and has ten 250 $\mu$m-thick gas gaps.
Signals are read out from two ends of strip with an active area of 50
cm$\times$2.5 cm in each. The detector was tested at FOPI in GSI, using the
secondary particles of proton beams ($E = 3.5 GeV$) colliding with a Pb target.
The results show that the LMRPC prototype has a time resolution of about
60$\sim$70 ps; the detecting efficiency is over 98% and the ratio of cross-talk
is lower than 2%. The detector also has a good spatial resolution of 0.36 cm
along the strip direction. | 1101.0224v1 |
2011-02-10 | Stimulated emission and absorption of photons in magnetic point contacts: toward metal-based spin-lasers | Point contacts between high anisotropy ferromagnetic SmCo5 and normal metal
Cu are used to achieve a strong spin-population inversion in the contact core.
Subjected to microwave irradiation in resonance with the Zeeman splitting in
Cu, the inverted spin-population relaxes through stimulated spin-flip photon
emission, detected as peaks in the point contact resistance. Resonant spin-flip
photon absorption is detected as resistance minima, corresponding to sourcing
the photon field energy into the electrical circuit. These results demonstrate
fundamental mechanisms that are potentially useful for designing metallic
spin-based lasers. | 1102.2167v1 |
2011-02-14 | Edge effect on resistance scaling rules in graphene nanostructures | We report an experimental investigation of the edge effect on the
room-temperature transport in graphene nanoribbon and graphene sheet (both
single-layer and bilayer). By measuring the resistance scaling behaviors at
both low and high carrier densities, we show that the transport of single-layer
nanoribbons lies in a strong localization regime, which can be attributed to an
edge effect. We find that this edge effect can be weakened by enlarging the
width, decreasing the carrier densities or adding an extra layer. From graphene
nanoribbon to graphene sheet, the data show a dimensional crossover of the
transport regimes possibly due to the drastic change of the edge effect. | 1102.2681v1 |
2011-02-20 | In situ TEM investigation of oxygen migration as a key mechanism for resistive switching in Pr0.7Ca0.3MnO3 | Low temperature growth Pr0.7Ca0.3MnO3 (PCMO) thin film showed high
performance in electric field induced resistance switching (RS). To understand
the micro-mechanism of RS in Metal/PCMO/Metal devices, structure evolution of
PCMO under external electric field monitored inside transmission electron
microscope (TEM) were performed. Evolution of the modulation stripe in as-grown
PCMO sample was investigated when applying electric field. The new-generated
modulation stripe gradually disappeared. These results indicate that oxygen ion
migration plays a key role in RS. | 1102.4044v3 |
2011-05-19 | Enhancement of the Superconducting Transition Temperature with Hydrostatic Pressure in Ca_{3}Ir_{4}Sn_{13} Single Crystals | We report high pressure magnetic susceptibility and electrical resistivity
measurements on Ca_{3}Ir_{4}Sn_{13} single crystals up to 60 kbar. These
measurements allow us to follow the evolution of the superconducting critical
temperature T_c, the resistivity anomaly temperature T*, the superconducting
coherence length and the Fermi velocity under pressure. The
pressure-temperature phase diagram constructed for Ca_{3}Ir_{4}Sn_{13} shows a
dome-shaped pressure dependence of T_c. The initial rise in T_c, which is
accompanied by a decrease in T*, is consistent with a reduction in the partial
gapping of the Fermi surface under pressure. | 1105.3941v1 |
2011-05-24 | Low Bias Negative Differential Resistance in Graphene Nanoribbon Superlattices | We theoretically investigate negative differential resistance (NDR) for
ballistic transport in semiconducting armchair graphene nanoribbon (aGNR)
superlattices (5 to 20 barriers) at low bias voltages V_SD < 500 mV. We combine
the graphene Dirac Hamiltonian with the Landauer-B\"uttiker formalism to
calculate the current I_SD through the system. We find three distinct transport
regimes in which NDR occurs: (i) a "classical" regime for wide layers, through
which the transport across band gaps is strongly suppressed, leading to
alternating regions of nearly unity and zero transmission probabilities as a
function of V_SD due to crossing of band gaps from different layers; (ii) a
quantum regime dominated by superlattice miniband conduction, with current
suppression arising from the misalignment of miniband states with increasing
V_SD; and (iii) a Wannier-Stark ladder regime with current peaks occurring at
the crossings of Wannier-Stark rungs from distinct ladders. We observe NDR at
voltage biases as low as 10 mV with a high current density, making the aGNR
superlattices attractive for device applications. | 1105.4850v2 |
2011-10-22 | Pressure Induced Metallization of BaMn2As2 | The temperature and pressure dependent electrical resistivity rho(T,P)
studies have been performed on BaMn2As2 single crystal in the 4.2 to 300 K
range upto of 8.2 GPa to investigate the evolution of its ground state
properties. The rho(T) shows a negative co-efficient of resistivity under
pressure upto 3.2 GPa. The occurrence of an insulator to metal transition (MIT)
in an external P ~4.5 GPa is indicated by a change in the temperature
co-efficient in the rho(T) data at ~36 K . However complete metallization in
entire temperature range is seen at a P~5.8 GPa. High pressure XRD studies
carried out at room temperature also shows an anomaly in the pressure versus
volume curve around P ~ 5 GPa, without a change in crystal structure,
indicative of an electronic transition. Further, a clear precipitous drop in
rho(T) at ~17 K is seen for P ~5.8 GPa which suggests the possibility of the
system going over to a superconducting ground state. | 1110.4969v2 |
2011-10-24 | Two coupled Josephson junctions: dc voltage controlled by biharmonic current | We study transport properties of two Josephson junctions coupled by an
external shunt resistance. One of the junction (say, the first) is driven by an
unbiased ac current consisting of two harmonics. The device can rectify the ac
current yielding a dc voltage across the first junction. For some values of
coupling strength, controlled by an external shunt resistance, a dc voltage
across the second junction can be generated. By variation of system parameters
like the relative phase or frequency of two harmonics, one can conveniently
manipulate both voltages with high efficiency, e.g., changing the dc voltages
across the first and second junctions from positive to negative values and vice
versa. | 1110.5287v3 |
2011-10-31 | Resistivity saturation in a weakly interacting 2D Fermi liquid at intermediate temperatures | We report a highly unusual temperature dependence in the magnetoresistance of
a weakly interacting high mobility 2D electron gas (2DEG) under a parallel
magnetic field and when the current is perpendicular to the field. While the
linear temperature dependence below 10 K and the exponential temperature
dependence above 40 K agree with existing theory of electron-phonon scattering,
a field induced resistivity saturation behaviour characterized by an almost
complete suppression of the temperature dependence is observed from
approximately 20 to 40 K, which is in sharp contrast to the phenomenology
observed when the current is parallel to the field. Possible origins of this
intriguing intermediate temperature phenomenon are discussed. | 1111.0011v2 |
2011-11-14 | Anomalous resistivity and the electron-polaron effect in the two-band Hubbard model with one narrow band | We search for anomalous normal and superconductive behavior in the two-band
Hubbard model with one narrow band. We analyze the influence of
electron-polaron effect and Altshuler-Aronov effect on effective mass
enhancement and scattering times of heavy and light components in the clean
case. We find anomalous behavior of resistivity at high temperatures
$T>W_{h}^{*}$ both in 3D and 2D situation. The SC instability in the model is
governed by enhanced Kohn-Luttinger effect for p-wave pairing of heavy
electrons via polarization of light electrons. | 1111.3135v1 |
2011-12-07 | Low carrier concentration crystals of the topological insulator Bi$_2$Te$_2$Se | We report the characterization of Bi$_2$Te$_2$Se crystals obtained by the
modified Bridgman and Bridgman-Stockbarger crystal growth techniques. X-ray
diffraction study confirms an ordered Se-Te distribution in the inner and outer
chalcogen layers, respectively, with a small amount of mixing. The crystals
displaying high resistivity ($> 1 \mathrm{\Omega cm}$) and low carrier
concentration ($\sim 5\times 10^{16}$/cm$^3$) at 4 K were found in the central
region of the long Bridgman-Stockbarger crystal, which we attribute to very
small differences in defect density along the length of the crystal rod.
Analysis of the temperature dependent resistivities and Hall coefficients
reveals the possible underlying origins of the donors and acceptors in this
phase. | 1112.1648v1 |
2011-12-22 | Field induced quantum-Hall ferromagnetism in suspended bilayer graphene | We have measured the magneto-resistance of freely suspended high-mobility
bilayer graphene. For magnetic fields $B>1$ T we observe the opening of a field
induced gap at the charge neutrality point characterized by a diverging
resistance. For higher fields the eight-fold degenerated lowest Landau level
lifts completely. Both the sequence of this symmetry breaking and the strong
transition of the gap-size point to a ferromagnetic nature of the insulating
phase developing at the charge neutrality point. | 1112.5368v2 |
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