1,762 research outputs found
Erratum: Theory of charge transport in diffusive normal metal/unconventional singlet superconductor contacts [Phys. Rev. B 69, 144519 (2004)]
Applied Science
Josephson current in unconventional superconductors through an Anderson impurity
Josephson current for a system consisting of an Anderson impurity weakly
coupled to two unconventional superconductors is studied and shown to be driven
by a surface zero energy (mid-gap) bound-state. The repulsive Coulomb
interaction in the dot can turn a junction into a 0-junction. This effect
is more pronounced in p-wave superconductors while in high-temperature
superconductors with symmetry it can exit for rather large
artificial centers at which tunneling occurs within a finite region.Comment: 4 pages 3.eps figure
The effective bandwidth problem revisited
The paper studies a single-server queueing system with autonomous service and
priority classes. Arrival and departure processes are governed by marked
point processes. There are buffers corresponding to priority classes,
and upon arrival a unit of the th priority class occupies a place in the
th buffer. Let , denote the quota for the total
th buffer content. The values are assumed to be large, and
queueing systems both with finite and infinite buffers are studied. In the case
of a system with finite buffers, the values characterize buffer
capacities.
The paper discusses a circle of problems related to optimization of
performance measures associated with overflowing the quota of buffer contents
in particular buffers models. Our approach to this problem is new, and the
presentation of our results is simple and clear for real applications.Comment: 29 pages, 11pt, Final version, that will be published as is in
Stochastic Model
Uniqueness of bounded solutions for the homogeneous Landau equation with a Coulomb potential
We prove the uniqueness of bounded solutions for the spatially homogeneous
Fokker-Planck-Landau equation with a Coulomb potential. Since the local (in
time) existence of such solutions has been proved by Arsen'ev-Peskov (1977), we
deduce a local well-posedness result. The stability with respect to the initial
condition is also checked
An ARPES view on the high-Tc problem: phonons vs spin-fluctuations
We review the search for a mediator of high-Tc superconductivity focusing on
ARPES experiment. In case of HTSC cuprates, we summarize and discuss a
consistent view of electronic interactions that provides natural explanation of
both the origin of the pseudogap state and the mechanism for high temperature
superconductivity. Within this scenario, the spin-fluctuations play a decisive
role in formation of the fermionic excitation spectrum in the normal state and
are sufficient to explain the high transition temperatures to the
superconducting state while the pseudogap phenomenon is a consequence of a
Peierls-type intrinsic instability of electronic system to formation of an
incommensurate density wave. On the other hand, a similar analysis being
applied to the iron pnictides reveals especially strong electron-phonon
coupling that suggests important role of phonons for high-Tc superconductivity
in pnictides.Comment: A summary of the ARPES part of the Research Unit FOR538,
http://for538.wmi.badw.d
From bound states to resonances: analytic continuation of the wave function
Single-particle resonance parameters and wave functions in spherical and
deformed nuclei are determined through analytic continuation in the potential
strength. In this method, the analyticity of the eigenvalues and eigenfunctions
of the Schroedinger equation with respect to the coupling strength is exploited
to analytically continue the bound-state solutions into the positive-energy
region by means of Pade' approximants of the second kind. The method is here
applied to single-particle wave functions of the and
nuclei. A comparison of the results with the direct solution of the
Schroedinger equation shows that the method can be confidently applied also in
coupled-channel situations requiring high numerical accuracy.Comment: 13 pages, 3 figure
A phenomenological theory of zero-energy Andreev resonant states
A conceptual consideration is given to a zero-energy state (ZES) at the
surface of unconventional superconductors. The reflection coefficients in
normal-metal / superconductor (NS) junctions are calculated based on a
phenomenological description of the reflection processes of a quasiparticle.
The phenomenological theory reveals the importance of the sign change in the
pair potential for the formation of the ZES. The ZES is observed as the
zero-bias conductance peak (ZBCP) in the differential conductance of NS
junctions. The split of the ZBCP due to broken time-reversal symmetry states is
naturally understood in the present theory. We also discuss effects of external
magnetic fields on the ZBCP.Comment: 12 page
Disappearance of Ensemble-Averaged Josephson Current in Dirty SNS Junctions of d-wave Superconductors
We discuss the Josephson current in superconductor / dirty normal conductor /
superconductor junctions, where the superconductors have pairing
symmetry. The low-temperature behavior of the Josephson current depends on the
orientation angle between the crystalline axis and the normal of the junction
interface. We show that the ensemble-averaged Josephson current vanishes when
the orientation angle is and the normal conductor is in the diffusive
transport regime. The -wave pairing symmetry is responsible for
this fact.Comment: 8 pages, 5 figure
Theory of charge transport in diffusive normal metal / unconventional singlet superconductor contacts
We analyze the transport properties of contacts between unconventional
superconductor and normal diffusive metal in the framework of the extended
circuit theory. We obtain a general boundary condition for the Keldysh-Nambu
Green's functions at the interface that is valid for arbitrary transparencies
of the interface. This allows us to investigate the voltage-dependent
conductance (conductance spectrum) of a diffusive normal metal (DN)/
unconventional singlet superconductor junction in both ballistic and diffusive
cases. For d-wave superconductor, we calculate conductance spectra numerically
for different orientations of the junctions, resistances, Thouless energies in
DN, and transparencies of the interface. We demonstrate that conductance
spectra exhibit a variety of features including a -shaped gap-like
structure, zero bias conductance peak (ZBCP) and zero bias conductance dip
(ZBCD). We show that two distinct mechanisms: (i) coherent Andreev reflection
(CAR) in DN and (ii) formation of midgap Andreev bound state (MABS) at the
interface of d-wave superconductors, are responsible for ZBCP, their relative
importance being dependent on the angle between the interface normal
and the crystal axis of d-wave superconductors. For , the ZBCP is due
to CAR in the junctions of low transparency with small Thouless energies, this
is similar to the case of diffusive normal metal / insulator /s-wave
superconductor junctions. With increase of from zero to , the
MABS contribution to ZBCP becomes more prominent and the effect of CAR is
gradually suppressed. Such complex spectral features shall be observable in
conductance spectra of realistic high- junctions at very low temperature
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