79 research outputs found
Multiple Superconducting Phases in New Heavy Fermion Superconductor PrOs4Sb12
The superconducting gap structure of recently discovered heavy fermion
superconductor PrOs4Sb12 was investigated by using thermal transport
measurements in magnetic field rotated relative to the crystal axes. We
demonstrate that a novel change in the symmetry of the superconducting gap
function occurs deep inside the superconducting state, giving a clear
indication of the presence of two distinct superconducting phases with twofold
and fourfold symmetries. We infer that the gap functions in both phases have a
point node singularity, in contrast to the familiar line node singularity
observed in almost all unconventional superconductors.Comment: 4 Pages, 4 Figure
Outbreak of West Nile virus infection, Volgograd Region, Russia, 1999.
From July 25 to October 1, 1999, 826 patients were admitted to Volgograd Region, Russia, hospitals with acute aseptic meningoencephalitis, meningitis, or fever consistent with arboviral infection. Of 84 cases of meningoencephalitis, 40 were fatal. Fourteen brain specimens were positive in reverse transcriptase-polymerase chain reaction assays, confirming the presence of West Nile/Kunjin virus
Assessment of the nephroprotective properties of the erythropoietin mimetic peptide and infliximab in kidney ischemia-reperfusion injury in rat
The present study aimed to investigate the protective effects of erythropoietin mimetic peptide (pHBSP) and infliximab on ischemic renal reperfusion injur. The experiment was performed on 70 white male Wistar laboratory rats which received recombinant erythropoietin, pHBSP, and inflixima
Non-universal equilibrium crystal shape results from sticky steps
The anisotropic surface free energy, Andreev surface free energy, and
equilibrium crystal shape (ECS) z=z(x,y) are calculated numerically using a
transfer matrix approach with the density matrix renormalization group (DMRG)
method. The adopted surface model is a restricted solid-on-solid (RSOS) model
with "sticky" steps, i.e., steps with a point-contact type attraction between
them (p-RSOS model). By analyzing the results, we obtain a first-order shape
transition on the ECS profile around the (111) facet; and on the curved surface
near the (001) facet edge, we obtain shape exponents having values different
from those of the universal Gruber-Mullins-Pokrovsky-Talapov (GMPT) class. In
order to elucidate the origin of the non-universal shape exponents, we
calculate the slope dependence of the mean step height of "step droplets"
(bound states of steps) using the Monte Carlo method, where p=(dz/dx,
dz/dy)$, and represents the thermal averag |p| dependence of , we
derive a |p|-expanded expression for the non-universal surface free energy
f_{eff}(p), which contains quadratic terms with respect to |p|. The first-order
shape transition and the non-universal shape exponents obtained by the DMRG
calculations are reproduced thermodynamically from the non-universal surface
free energy f_{eff}(p).Comment: 31 pages, 21 figure
Ground State and Excitations of Spin Chain with Orbital Degeneracy
The one dimensional Heisenberg model in the presence of orbital degeneracy is
studied at the SU(4) symmetric viewpoint by means of Bethe ansatz. Following
Sutherland's previous work on an equivalent model, we discuss the ground state
and the low-lying excitations more extensively in connection to the spin
systems with orbital degeneracy. We show explicitly that the ground state is a
SU(4) singlet. We study the degeneracies of the elementary excitations and the
spectra of the generalized magnons consisting of these excitations. We also
discuss the complex 2-strings in the context of the Bethe ansatz solutions.Comment: Revtex, 9 pages, 3 figures; typos correcte
NbS: A unique quasi one-dimensional conductor with three charge density wave transitions
Through transport, compositional and structural studies, we review the
features of the charge-density wave (CDW) conductor of NbS (phase II). We
highlight three central results: 1) In addition to the previously reported CDW
transitions at = 360\,K and = 150\,K, another CDW transition
occurs at a much higher temperature = 620-650\,K; evidence for the
non-linear conductivity of this CDW is presented. 2) We show that CDW
associated with the - transition arises from S vacancies acting as
donors. Such a CDW transition has not been observed before. 3) We show
exceptional coherence of the -CDW at room-temperature. Additionally, we
report on the effects of uniaxial strain on the CDW transition temperatures and
transport.Comment: 16 pages, 18 figure
{\em Ab Initio} Calculations of in Type-II Superconductors: Basic Formalism and Model Calculations
Detailed Fermi-surface structures are essential to describe the upper
critical field in type-II superconductors, as first noticed by
Hohenberg and Werthamer [Phys. Rev. {\bf 153}, 493 (1967)] and shown explicitly
by Butler for high-purity cubic Niobium [Phys. Rev. Lett. {\bf 44}, 1516
(1980)]. We derive an equation for classic type-II superconductors
which is applicable to systems with anisotropic Fermi surfaces and/or energy
gaps under arbitrary field directions. It can be solved efficiently by using
Fermi surfaces from {\em ab initio} electronic-structure calculations. Thus, it
is expected to enhance our quantitative understanding on . Based on the
formalism, we calculate curves for Fermi surfaces of a
three-dimensional tight-binding model with cubic symmetry, an isotropic gap,
and no impurity scatterings. It is found that, as the Fermi surface approaches
to the Brillouin zone boundary, the reduced critical field ,
which is normalized by the initial slope at , is enhanced significantly
over the curve for the spherical Fermi surface with a marked upward curvature.
Thus, the Fermi-surface anisotropy can be a main source of the upward curvature
in near .Comment: 16 pages, 4 figures, results from model calculations include
Nodal Structure of Unconventional Superconductors Probed by the Angle Resolved Thermal Transport Measurements
Over the past two decades, unconventional superconductivity with gap symmetry
other than s-wave has been found in several classes of materials, including
heavy fermion (HF), high-T_c, and organic superconductors. Unconventional
superconductivity is characterized by anisotropic superconducting gap
functions, which may have zeros (nodes) along certain directions in the
Brillouin zone. The nodal structure is closely related to the pairing
interaction, and it is widely believed that the presence of nodes is a
signature of magnetic or some other exotic, rather than conventional
phonon-mediated, pairing mechanism. Therefore experimental determination of the
gap function is of fundamental importance. However, the detailed gap structure,
especially the direction of the nodes, is an unresolved issue in most
unconventional superconductors. Recently it has been demonstrated that the
thermal conductivity and specific heat measurements under magnetic field
rotated relative to the crystal axes are a powerful method for determining the
shape of the gap and the nodal directions in the bulk. Here we review the
theoretical underpinnings of the method and the results for the nodal structure
of several unconventional superconductors, including borocarbide YNiBC,
heavy fermions UPdAl, CeCoIn, and PrOsSb, organic
superconductor, -(BEDT-TTF)Cu(NCS), and ruthenate
SrRuO, determined by angular variation of the thermal conductivity and
heat capacity.Comment: topical review, 55 pages, 35 figures. Figure quality has been reduced
for submission to cond-mat, higher quality figures available from the authors
or from the publishe
Melting and transverse depinning of driven vortex lattices in the periodic pinning of Josephson junction arrays
We study the non-equilibrium dynamical regimes of a moving vortex lattice in
the periodic pinning of a Josephson junction array (JJA) for {\it finite
temperatures} in the case of a fractional or submatching field. We obtain a
phase diagram for the current driven JJA as a function of the driving current I
and temperature T. We find that when the vortex lattice is driven by a current,
the depinning transition at and the melting transition at
become separated even for a field for which they coincide in equilibrium. We
also distinguish between the depinning of the vortex lattice in the direction
of the current drive, and the {\it transverse depinning} in the direction
perpendicular to the drive. The transverse depinning corresponds to the onset
of transverse resistance in a moving vortex lattice at a given temperature
. For driving currents above the critical current we find that the
moving vortex lattice has first a transverse depinning transition at low T, and
later a melting transition at a higher temperature, .Comment: 17 pages, 19 figure
The Quantum Vlasov Equation and its Markov Limit
The adiabatic particle number in mean field theory obeys a quantum Vlasov
equation which is nonlocal in time. For weak, slowly varying electric fields
this particle number can be identified with the single particle distribution
function in phase space, and its time rate of change is the appropriate
effective source term for the Boltzmann-Vlasov equation. By analyzing the
evolution of the particle number we exhibit the time structure of the particle
creation process in a constant electric field, and derive the local form of the
source term due to pair creation. In order to capture the secular Schwinger
creation rate, the source term requires an asymptotic expansion which is
uniform in time, and whose longitudinal momentum dependence can be approximated
by a delta function only on long time scales. The local Vlasov source term
amounts to a kind of Markov limit of field theory, where information about
quantum phase correlations in the created pairs is ignored and a reversible
Hamiltonian evolution is replaced by an irreversible kinetic one. This
replacement has a precise counterpart in the density matrix description, where
it corresponds to disregarding the rapidly varying off-diagonal terms in the
adiabatic number basis and treating the more slowly varying diagonal elements
as the probabilities of creating pairs in a stochastic process. A numerical
comparison between the quantum and local kinetic approaches to the dynamical
backreaction problem shows remarkably good agreement, even in quite strong
electric fields, over a large range of times.Comment: 49 pages, RevTex/LaTeX2e, 8 .eps figures included in 404KB .gz file
(~3MB total uncompressed). Replacement added \tightenpages command to reduce
from 67 to 49 p
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