28 research outputs found
The effect of nonmagnetic impurities on the local density of states in s-wave superconductors
We study the effect of nonmagnetic impurities on the local density of states
(LDOS) in s-wave superconductors. The quasiclassical equations of
superconductivity are solved selfconsistently to show how LDOS evolves with
impurity concentration. The spatially averaged zero-energy LDOS is a linear
function of magnetic induction in low fields, N(E=0)=cB/H_{c2}, for all
impurity concentration. The constant of proportionality "c" depends weakly on
the electron mean free path. We present numerical data for differential
conductance and spatial profile of zero-energy LDOS which can help in
estimating the mean free path through the LDOS measurement.Comment: 7 pages, 7 figures (high quality color figure available on request
Anisotropic Diamagnetic Response in Type-II Superconductors with Gap and Fermi-Surface Anisotropies
Effects of anisotropic gap structures on a diamagnetic response are
investigated in order to demonstrate that the field-angle-resolved
magnetization () measurement can be used as a spectroscopic method
to detect gap structures. Our microscopic calculation based on the
quasiclassical Eilenberger formalism reveals that in a
superconductor with four-fold gap displays a four-fold oscillation reflecting
the gap and Fermi surface anisotropies, and the sign of this oscillation
changes at a field between and . As a prototype of
unconventional superconductors, magnetization data for borocarbides are also
discussed.Comment: 5 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
Effect of field dependent core size on reversible magnetization of high- superconductors
The field dependence of the vortex core size is incorporated in the
London model, in order to describe reversible magnetization for a
number of materials with large Ginzburg-Landau parameter . The
dependence is directly related to deviations in from linear
behavior prescribed by the standard London model. A simple method to extract
from the magnetization data is proposed. For most materials examined,
so obtained decreases with increasing field and is in qualitative
agreement both with behavior extracted from SR and small angle neutron
scattering data and with that predicted theoretically
Quasi-Classical Calculation of the Mixed-State Thermal Conductivity in s-Wave and d-Wave Superconductors
To see how superconducting gap structures affect the longitudinal component
of mixed-state thermal conductivity kappa_{xx}(B), the magnetic-field
dependences of kappa_{xx}(B) in s-wave and d-wave superconductors are
investigated. Calculations are performed on the basis of the quasi-classical
theory of superconductivity by fully taking account of the spatial variation of
the normal Green's function, neglected in previous works, by the
Brandt-Pesch-Tewordt approximation. On the basis of our result, we discuss the
possibility of kappa_{xx}(B) measurement as a method of probing the gap
structure.Comment: To appear in J. Phys. Soc. Jp
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
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
Field-angle-dependent specific heat measurements and gap determination of a heavy fermion superconductor URu2Si2
To identify the superconducting gap structure in URu2Si2 we perform
field-angle-dependent specific heat measurements for the two principal
orientations in addition to field rotations, and theoretical analysis based on
microscopic calculations. The Sommerfeld coefficient \gamma(H)'s in the mixed
state exhibit distinctively different field-dependence. This comes from point
nodes and substantial Pauli paramagnetic effect of URu2Si2. These two features
combined give rise to a consistent picture of superconducting properties,
including a possible first order transition of Hc2 at low temperatures.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let
Influence of gap structures to specific heat in oriented magnetic fields: Application to the orbital dependent superconductor, SrRuO
We discuss influence of modulation of gap function and anisotropy of Fermi
velocity to field angle dependences of upper critical field, , and
specific heat, , on the basis of the approximate analytic solution in the
quasiclassical formalism. Using 4-fold modulation of the gap function and the
Fermi velocity in the single-band model, we demonstrate field and temperature
dependence of oscillatory amplitude of and . We apply the method to
the effective two-band model to discuss the gap structure of SrRuO,
focusing on recent field angle-resolved experiments. It is shown that the gap
structures with the intermediate magnitude of minima in direction for
band, and tiny minima of gaps in directions for and
bands give consistent behaviors with experiments. The interplay of the
above two gaps also explains the anomalous temperature dependence of in-plane
anisotropy, where the opposite contribution from the passive
band is pronounced near .Comment: 7 pages, 11 figures in JPSJ forma