229 research outputs found
NMR relaxation time around a vortex in stripe superconductors
Site-dependent NMR relaxation time is calculated in the vortex
state using the Bogoliubov-de Gennes theory, taking account of possible
"field-induced stripe'' states in which the magnetism arises locally around a
vortex core in d-wave superconductivity. The recently observed huge enhancement
below at a core site in TlBaCuO is
explained. The field-induced stripe picture explains consistently other
relevant STM and neutron experiments.Comment: 4 pages, 4 figure
Specific heat and low-lying excitations in the mixed state for a type II superconductor
Low temperature behavior of the electronic specific heat in the mixed
state is by the self-consistent calculation of the Eilenberger theory. In
addition to -term ( is a Sommerfeld coefficient), has
significant contribution of -term intrinsic in the vortex state. We
identify the origin of the -term as (i) V-shape density of states in the
vortex state and (ii) Kramer-Pesch effect of vortex core shrinking upon
lowering . These results both for full-gap and line node cases reveal that
the vortex core is a richer electronic structure beyond the normal core
picture.Comment: Accepted in Phys. Rev. B. 5 pages, 5 figure
- and -wave components induced around a vortex in -wave superconductors
Vortex structure of -wave superconductors is microscopically
analyzed in the framework of the quasi-classical Eilenberger equations. If the
pairing interaction contains an -wave (-wave) component in addition
to a -wave component, the -wave (-wave) component of
the order parameter is necessarily induced around a vortex in
-wave superconductors. The spatial distribution of the induced
-wave and -wave components is calculated. The -wave component has
opposite winding number around vortex near the -vortex core and
its amplitude has the shape of a four-lobe clover. The amplitude of
-component has the shape of an octofoil. These are consistent with
results based on the GL theory.Comment: RevTex,9 pages, 6 figures in a uuencoded fil
Reentrant vortex lattice transformation in four-fold symmetric superconductors
The physics behind the rhombicsquarerhombic flux line lattice
transformation in increasing fields is clarified on the basis of Eilenberger
theory. We demonstrate that this reentrance observed in LuNiBC is due
to intrinsic competition between superconducting gap and Fermi surface
anisotropies. The calculations reproduce not only it but also predict yet not
found lock-in transition to a square lattice with different orientation in
higher field. In view of physical origin given, this sequence of transitions is
rather generic to occur in four-fold symmetric superconductors.Comment: 5 pages, 4 figures,submitted to Phys. Rev. Let
Theory of vortex excitation imaging via an NMR relaxation measurement
The temperature dependence of the site-dependent nuclear spin relaxation time
T_1 around vortices is studied in s-wave and d-wave superconductors.Reflecting
low energy electronic excitations associated with the vortex core, temperature
dependences deviate from those of the zero-field case, and T_1 becomes faster
with approaching the vortex core. In the core region, T_1^{-1} has a new peak
below T_c. The NMR study by the resonance field dependence may be a new method
to prove the spatial resolved vortex core structure in various superconductors.Comment: 5 pages, 3 figure
Vortex state in double transition superconductors
Novel vortex phase and nature of double transition field are investigated by
two-component Ginzburg-Landau theory in a situation where fourfold-twofold
symmetric superconducting double transition occurs. The deformation from 60
degree triangular vortex lattice and a possibility of the vortex sheet
structure are discussed. In the presence of the gradient coupling, the
transition changes to a crossover at finite fields. These characters are
important to identify the multiple superconducting phase in PrOs_4_Sb_12.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
Induced Kramer-Pesch-Effect in a Two Gap Superconductor: Application to MgB2
The size of the vortex core in a clean superconductor is strongly temperature
dependent and shrinks with decreasing temperature, decreasing to zero for T ->
0. We study this so-called Kramer-Pesch effect both for a single gap
superconductor and for the case of a two gap superconductor using parameters
appropriate for Magnesium Diboride. Usually, the Kramer-Pesch effect is absent
in the dirty limit. Here, we show that the Kramer-Pesch effect exists in both
bands of a two gap superconductor even if only one of the two bands is in the
clean limit and the other band in the dirty limit, a case appropriate for MgB2.
In this case an induced Kramer-Pesch effect appears in the dirty band. Besides
numerical results we also present an analytical model for the spatial variation
of the pairing potential in the vicinity of the vortex center that allows a
simple calculation of the vortex core radius even in the limit T -> 0.Comment: 12 pages, 12 figure
Thermodynamics and magnetic field profiles in low-kappa type-II superconductors
Two-dimensional low-kappa type-II superconductors are studied numerically
within the Eilenberger equations of superconductivity. Depending on the
Ginzburg-Landau parameter \kappa=\lambda/\xi vortex-vortex interaction can be
attractive or purely repulsive. The sign of interaction is manifested as a
first (second) order phase transition from Meissner to the mixed state.
Temperature and field dependence of the magnetic field distribution in
low-kappa type-II superconductors with attractive intervortex interaction is
calculated. Theoretical results are compared to the experiment.Comment: 4 pages, 3 figure
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