4,214 research outputs found
Nonlinear response and scaling law in the vortex state of d-wave superconductors
We study the field dependence of the quasi-particle density of states, the
thermodynamics and the transport properties in the vortex state of d-wave
superconductors when a magnetic field is applied perpendicular to the
conducting plane, specially for the low field and the low temperature compared
to the upper critical field and transition temperature, respectively, and . Both the superfluid density and the spin
susceptibility exhibit the characteristic -field dependence, while
the nuclear spin lattice relaxation rate T and the thermal
conductivity are linear in field . With increasing temperature, these
quantities exhibit the scaling behavior in . The present theory
applies to 2D -wave superconductor as well; a possible candidate of the
superconductivity in SrRuO.Comment: 11 pages, 4 figure
Low-lying excitations around a single vortex in a d-wave superconductor
A full quantum-mechanical treatment of the Bogoliubov-de Gennes equation for
a single vortex in a d-wave superconductor is presented. First, we find
low-energy states extended in four diagonal directions, which have no
counterpart in a vortex of s-wave superconductors. The four-fold symmetry is
due to 'quantum effect', which is enhanced when is small. Second,
for , a peak with a large energy gap is
found in the density of states, which is due to the formation of the lowest
bound states.Comment: 7pages, Revte
Possible f-wave superconductivity in SrRuO?
Until recently it has been believed that the superconductivity in
SrRuO is described by p-wave pairing. However, both the recent specific
heat and the magnetic penetration depth measurements on the purest single
crystals of SrRuO appear to be explained more consistently in terms of
f-wave superconductivity. In order to further this hypothesis, we study
theoretically the thermodynamics and thermal conductivity of f-wave
superconductors in a planar magnetic field. We find the simple expressions for
these quantities when and , which should be
readily accessible experimentally.Comment: 6 pages, 2 figure
Half quantum vortex in superfluid He-A phase in parallel plate geometry
The half quantum vortex(HQV) in condensate has been studied, since it was
predicted by Salomaa and Volovik in superfluid He-A phase. However, an
experimental evidence for its existence has not been reported so far. Motivated
by a recent experimental report by Yamashita et al\cite{yamashita}, we study
the HQVs in superfluid He confined between two parallel plates with a gap D
10 m in the presence of a magnetic field H 26 mT
perpendicular to the parallel plates. We find that the bound HQVs are more
stable than the singular vortices and free pairs of HQVs, when the rotation
perpendicular to the parallel plates is below the critical speed, 2 rad/s. The bound pair of HQVs accompanies the tilting of -vector out of the plane, which leads to an additional absorption in NMR
spectra. Our study appears to describe the temperature and rotation dependence
of the observed satellite NMR signal, which supports the existence of the HQVs
in He.Comment: 5 pages, 5 figure
Gap Symmetry an Thermal Conductivity in Nodal Superconductors
There are now many nodal superconductors in heavy fermion (HF) systems,
charge conjugated organic metals, high Tc cuprates and ruthenates. On the other
hand only few of them have a well established gap function. We present here a
study of the angular dependent thermal conductivity in the vortex state of some
of the nodal superconductors. We hope it will help to identify the nodal
directions in the gap function of UPd_2Al_3, UNi_2Al_3, UBe_13 and URu_2Si_2.Comment: 4 pages, 5 figure
Supercurrent in Nodal Superconductors
In recent years, a number of nodal superconductors have been identified;
d-wave superconductors in high T_c cuprates, CeCoIn, and
\kappa-(ET)_2Cu(NCS)_2, 2D f-wave superconductor in Sr_2RuO_4 and hybrid
s+g-wave superconductor in YNi_2B_2C. In this work we conduct a theoretical
study of nodal superconductors in the presence of supercurrent. For simplicity,
we limit ourselves to d-wave and 2D f-wave superconductors. We compute the
quasiparticle density of states and the temperature dependence of the depairing
critical current in nodal superconductors, both of which are accessible
experimentally.Comment: revtex4, 6 pages, 7 figures; fixed typos, updated references, trimmed
introductio
Theory of the critical current in two-band superconductors with application to MgB2
Using a Green's function formulation of the superfluid current j_s, where a
momentum q_s is applied to the Cooper pair, we have calculated j_s as a
function of q_s, temperature, and impurity scattering for a two-band
superconductor. We consider both renormalized BCS and full strong-coupling
Eliashberg theory. There are two peaks in the current as a function of q_s due
to the two energy scales for the gaps and this can give rise to non-standard
behavior for the critical current. The critical current j_c, which is given as
the maximum in j_s, can exhibit a kink as a function of temperature as the
maximum is transferred from one peak to other. Other temperature variations are
also possible and the universal BCS behavior is violated. The details depend on
the material parameters of the system, such as the amount of coupling between
the bands, the gap anisotropy, the Fermi velocities, and the density of states
of each band. The Ginzburg-Landau relation between j_c, the penetration depth
lambda_L and thermodynamic critical field H_c, is modified. Using Eliashberg
theory with the electron-phonon spectral densities given from bandstructure
calculations, we have applied our calculations for j_s and j_c to the case of
MgB2 and find agreement with experiment.Comment: 13 pages, 7 figures, submitted to PR
Superconducting Gap Structure of kappa-(BEDT-TTF)2Cu(NCS)2 Probed by Thermal Conductivity Tensor
The thermal conductivity of organic superconductor kappa-(BEDT-TTF)2Cu(NCS)2
(Tc =10.4 K) has been studied in a magnetic field rotating within the 2D
superconducting planes with high alignment precision. At low temperatures (T <
0.5 K), a clear fourfold symmetry in the angular variation, which is
characteristic of a d-wave superconducting gap with nodes along the directions
rotated 45 degrees relative to the b and c axes of the crystal, was resolved.
The determined nodal structure is inconsistent with recent theoretical
predictions of superconductivity induced by the antiferromagnetic spin
fluctuation.Comment: 5 pages, 4 figures, to be published in Phys. Rev. Let
Thermal conductivity in B- and C- phase of UPt_3
Although the superconductivity in UPt_3 is one of the most well studied,
there are still lingering questions about the nodal directions in the B and C
phase in the presence of a magnetic field. Limiting ourselves to the low
temperature regime (T<<Delta(0)), we study the magnetothermal conductivity with
in semiclassical approximation using Volovik's approach. The angular dependence
of the magnetothermal conductivity for an arbitrary field direction should
clarify the nodal structure in UPt_3.Comment: 4 pages, 5 figure
Andreev scattering in nanoscopic junctions at high magnetic fields
We report on the measurement of multiple Andreev resonances at atomic size
point contacts between two superconducting nanostructures of Pb under magnetic
fields higher than the bulk critical field, where superconductivity is
restricted to a mesoscopic region near the contact. The small number of
conduction channels in this type of contacts permits a quantitative comparison
with theory through the whole field range. We discuss in detail the physical
properties of our structure, in which the normal bulk electrodes induce a
proximity effect into the mesoscopic superconducting part.Comment: 4 page
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