1,361 research outputs found
Charged and uncharged vortices in quasiclassical theory
The charging effect of a superconducting vortex core is very important for
transport properties of superconducting vortices. The chiral p-wave
superconductor, known as a topological superconductor (SC), has a Majorana
fermion in a vortex core and the charging effect has been studied using
microscopic Bogoliubov-de Gennes (BdG) theory. According to calculations based
on the BdG theory, one type of the vortex is charged as well as the vortex of
the s-wave SC, while the other is uncharged. We reproduce this interesting
charging effect using an augmented quasiclassical theory in chiral p-wave SCs,
by which we can deal with particle-hole asymmetry in the quasiclassical
approximation.Comment: 6 pages, 2 figure
Impurity Effects on Caroli-de Gennes-Matricon Mode in a Vortex Core in Superconductors
We develop a scheme of Gor'kov Green's functions to treat impurity effects on
Caroli-de Gennes-Matricon (CdGM) mode in superconductors (SCs) by improving the
Kopnin-Kravtsov scheme with respect to the coherence factors and applicability
to various SCs. We can study the impurity effects keeping the discreteness of
the energy spectrum in contrast to the quasiclassical theory. We can thus apply
this scheme to the SCs with the small quasiclassical parameter
(which is the product of the Fermi wavenumber
and the coherence length in pure SC at zero
temperature) and/or superclean regime
( and denote, respectively, the level spacing of
the CdGM mode called minigap and the relaxation time for CdGM mode and we take
). We investigate the impurity effects as a white noise for a vortex
in an s-wave SC and two types of vortices in a chiral p-wave SC, for various
values of the quasiclassical parameters and impurity strengths (from moderately
clean regime to superclean regime), and confirm the validity of this scheme.Comment: 8 pages, 6 figure
Impurity Effects on Bound States in the Vortex Core of Topological S-wave Superconductor
We study the impurity effects on the Caroli-de Gennes-Matricon (CdGM) states,
particularly on the level spacings in a vortex core in topological s-wave
superconductor (SC) by two means, numerically and analytically. The topological
s-wave SC belongs to the same class as a chiral p-wave SC and thus there are
two inequivalent vortices in terms of any symmetry operation. We take into
account this inequivalence and numerically calculate the scattering rates based
on an improved version of Kopnin-Kravtsov (iKK) scheme, which enables us to
treat the discrete levels in the presence of white-noise disorder. We also
construct the Andreev equation for the topological s-wave SC and obtain the
Andreev bound states analytically. We use a correspondence between the wave
functions for the Bogoliubov-de Gennes equation and the Andreev equation in the
iKK scheme and deduce the formula of scattering rates described by the wave
function for the Andreev equation. With this formula, we discuss the origin of
impurity scattering rates for CdGM states of topological s-wave SC and the
dependence on the types of vortices related to the inequivalence.Comment: 10 pages, 6 figure
Exact Result on Hole Dynamics of One-Dimensional Supersymmetric t-J Model with Long Range Interaction
We obtain an exact result on single hole dynamics in one-dimensional
Mott-insulators through the study on the supersymmetric t-J model with long
range interaction at half-filling. We calculate the expression G_{1s1h}(x,t)
for one spinon one holon contribution to the hole propagator. We find that
G_{1s1h}(x=0,t=0)=3/8, which amounts to 75% of the spin-fixed mean particle
density 1/2.Comment: RevTex, 5pages, 2figure
Kramer-Pesch effect in chiral p-wave superconductors
The pair-potential and current density around a single vortex of the
two-dimensional chiral p-wave superconductor with {\mib d}={\mib z}(p_x \pm
\iu p_y) are determined self-consistently within the quasiclassical theory of
superconductivity. Shrinking of the vortex core at low temperatures are
considered numerically and analytically. Temperature-dependences of the spatial
variation of pair-potential and circular current around the core and density of
states at zero energy are the same as those in the isotropic s-wave case. When
the senses of vorticity and chirality are opposite, however, we find two novel
results; 1) the scattering rate due to non-magnetic impurities is considerably
suppressed, compared to that in the s-wave vortex. From this observation, we
expect that the chiral p-wave superconductors provide the best chance to
observe the shrinking of the vortex ("Kramer-Pesch effect") experimentally. 2)
The pair-potential of chiral p-wave superconductors inside vortex core recovers
a combined time-reversal-Gauge symmetry, although this symmetry is broken in
the region far from the vortex core. This local recovery of symmetry leads to
the suppression of the impurity effect inside vortex core.Comment: 9 pages 15 figures, submitted to J. Phys. Soc. Jp
Mixing of odd- and even-frequency pairings in strongly correlated electron systems under magnetic field
Even- and odd-frequency superconductivity coexist due to broken time-reversal
symmetry under magnetic field. In order to describe this mixing, we extend the
linearized Eliashberg equation for the spin and charge fluctuation mechanism in
strongly correlated electron systems. We apply this extended Eliashberg
equation to the odd-frequency superconductivity on a quasi-one-dimensional
isosceles triangular lattice under in-plane magnetic field and examine the
effect of the even-frequency component.Comment: 5 pages, 4 figure
Transmission of Excitations in a Spin-1 Bose-Einstein Condensate through a Barrier
We investigate tunneling of excitations across a potential barrier separating
two spin-1 Bose-Einstein condensates. Using the mean-field theory at the
absolute zero temperature, we determine transmission coefficients of
excitations in the saturated magnetization state and unsaturated magnetization
states. All excitations except the quadrupolar spin mode in the saturated
magnetization state show the anomalous tunneling phenomenon characterized as
perfect tunneling in the low momentum limit through a potential barrier. The
quadrupolar spin mode in the saturated magnetization state, whose spectrum is
massive, shows total reflection. We discuss properties common between
excitations showing the anomalous tunneling phenomenon. Excitations showing
perfect tunneling have gapless spectrum in the absence of the magnetic field,
and their wave functions in the low energy limit are the same as the condensate
wave function.Comment: 45 pages, 16 figure
Fractional Exclusion Statistics for the t-J Model
We construct thermodynamics of the one-dimensional supersymmetric {\it t-J}
model with the interaction and hopping. The thermodynamics is
described exactly in terms of free spinons and holons obeying Haldane's
fractional exclusion statistics at all temperatures. Moreover, at low
temperatures the semionic spinons and holons decouple resulting in the
spin-charge separation in thermodynamic properties. We obtain explicit results
for the spin and charge susceptibilities and specific heat, and interpret them
in terms of the fractional exclusion statistics. Extension to the
multi-component {\it t-J} model shows that the excitations obey either
fractional statistics for g-ons with partial polarization of components, or the
parafermionic one without polarization.Comment: 27 pages, using jpsj.sty, 9 figures on reques
Coherence Effects of Caroli-de Gennes-Matricon Modes in Nodal Topological Superconductors
Coherence effects by the impurity scattering of Caroli--de Gennes--Matricon
(CdGM) modes in a vortex for nodal topological superconductors have been
studied. The coherence effects reflect a topological number defined on a
particular momentum space avoiding the superconducting gap nodes. First, we
analytically derived the eigenvalue and eigenfunction of the CdGM modes,
including the zero-energy modes, in a nodal topological superconducting state
without impurities, where we focused on a possible superconducting state of
UPt as an example. Then, we studied impurity effects on the CdGM modes by
introducing the impurity self-energy, which are dominated by the coherence
factor depending on the eigenfunction of the CdGM modes. For the zero-energy
CdGM modes, the coherence factor vanishes in a certain momentum range, which is
guaranteed by topological invariance characterized by the one-dimensional
winding number.Comment: 5 pages, 2 figures + 5 pages (supplementary material), published
versio
DC conductivity in an s-wave superconducting single vortex system
We study dynamics of a two-dimensional s-wave superconductor in the presence
of a moving single vortex. Our analysis is based on the quasiclassical theory
including the Hall term, generalized by Kita[T. Kita, PRB, 64, 054503 (2001)].
We numerically calculate the linear response of a moving single vortex driven
by a dc external current in a self-consistent way, in the sense that Dyson
equation, gap equation, Maxwell equations and generalized quasiclassical
equation are solved simultaneously. We obtain Hall conductivity induced by
vortex motion using the generalized quasiclassical equation, while we confirm
that it vanishes in the conventional quasiclassical equation.Comment: 7 pages, 4 figure
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