435 research outputs found
Finite Density of States in a Mixed State of d_x^2-y^2+id_xy Superconductor
We have calculated the density of states of quasiparticles in a
d_x^2-y^2+id_xy superconductor, and show that in the mixed state the
quasiparticle spectrum remains gapless because of the Doppler shift by
superflow. It was found that if the d_{xy} order gap
as suggested by experiments, then thermal conductivity in accord with experimental data at lowest temperatures. This is an
appended version of the paper published in Phys. Rev. {\bf B 59}, 6024, (1999).
We now also discuss the disorder effects and analyze the H log H crossover at
small fields. We argue that H log H regime is present and disorder effect is
dominant as the field-induced seconary gap is small at small fields.Comment: This is an appended version of the paper published in Phys. Rev. {\bf
B 59}, 6024, (1999). We now also discuss the disorder effects and analyze the
H log H crossover at small fields. 3 pages, Latex file with 2 eps figure
file
Fluctuation Superconductivity in Mesoscopic Aluminum Rings
Fluctuations are important near phase transitions, where they can be
difficult to describe quantitatively. Superconductivity in mesoscopic rings is
particularly intriguing because the critical temperature is an oscillatory
function of magnetic field. There is an exact theory for thermal fluctuations
in one-dimensional superconducting rings, which are therefore expected to be an
excellent model system. We measure the susceptibility of many rings, one ring
at a time, using a scanning SQUID that can isolate magnetic signals from seven
orders of magnitude larger background applied flux. We find that the
fluctuation theory describes the results and that a single parameter
characterizes the ways in which the fluctuations are especially important at
magnetic fields where the critical temperature is suppressed.Comment: Reprinted with permission from AAA
Anisotropic thermodynamics of d-wave superconductors in the vortex state
We show that the density of states and the thermodynamic properties of a 2D
d-wave superconductor in the vortex state with applied magnetic field
in the plane depend on the angle between and the order parameter nodes.
Within a semiclassical treatment of the extended quasiparticle states, we
obtain fourfold oscillations of the specific heat, measurement of which
provides a simple probe of gap symmetry. The frequency dependence of the
density of states and the temperature dependence of thermodynamic properties
obey different power laws for field in the nodal and anti-nodal direction. The
fourfold pattern is changed to twofold when orthorhombicity is considered.Comment: 5 pages, figures included, minor changes, published versio
Evidence for field-induced excitations in low-temperature thermal conductivity of Bi_2Sr_2CaCu_2O_8
The thermal conductivity ,, of Bi_2Sr_2CaCu_2O_8 was studied as a
function of magnetic field. Above 5 K, after an initial decrease,
presents a kink followed by a plateau, as recently reported by Krishana et al..
By contrast, below 1K, the thermal conductivity was found to \emph{increase}
with increasing field. This behavior is indicative of a finite density of
states and is not compatible with the existence of a field-induced fully gapped
state which was recently proposed to describe the
plateau regime. Our low-temperature results are in agreement with recent works
predicting a field-induced enhancement of thermal conductivity by Doppler shift
of quasi-particle spectrum.Comment: 4 pages including 4 eps figures, submitted to Phys. Rev. Let
Combined Paramagnetic and Diamagnetic Response of YBCO
It has been predicted that the zero frequency density of states of YBCO in
the superconducting phase can display interesting anisotropy effects when a
magnetic field is applied parallel to the copper-oxide planes, due to the
diamagnetic response of the quasi-particles. In this paper we incorporate
paramagnetism into the theory and show that it lessens the anisotropy and can
even eliminate it altogether. At the same time paramagnetism also changes the
scaling with the square root of the magnetic field first deduced by Volovik
leading to an experimentally testable prediction. We also map out the analytic
structure of the zero frequency density of states as a function of the
diamagnetic and paramagnetic energies. At certain critical magnetic field
values we predict kinks as we vary the magnetic field. However these probably
lie beyond currently accessible field strengths
Quasiparticle spectrum in the vortex state of d-wave superconductors
Quasiparticle spectrum associated with the nodal structure in d-wave
superconductors is of great interest. We study theoretically the quasi-particle
spectrum in a planar magnetic field, where the effect of the magnetic field is
treated in terms of the Doppler shift. We obtain the angular dependent specific
heat in the presence of a planar magnetic field and impurities, both in the
superclean limit (Gamma/Delta << H/H_{c2}<< 1) and in the clean limit (H/H_{c2}
<< Gamma/Delta <<1). Also a similar analysis is used for the thermal
conductivity tensor within the a-b plane. In particular, in contrast to the
earlier works, we find a fourfold symmetry term in \kappa_{\parallel} and
\kappa_{\perp} \sim -H \sin(2\theta) where kappa_{perp} are the diagonal- and
the off-diagonal components of the thermal conductivity tensor and \theta is
the angle between the heat current and the magnetic field.Comment: RevTex, 5 pages, 5 postscript figure
Transport Properties of d-Wave Superconductors in the Vortex State
We calculate the magnetic field dependence of quasiparticle transport
properties in the vortex state of a d-wave superconductor arising solely from
the quasiparticle's Doppler shift in the superflow field surrounding the
vortex. Qualitative features agree well with experiments on cuprate and heavy
fermion superconductors at low fields and temperatures. We derive scaling
relations in the variable valid at sufficiently low temperatures
and fields , but show that these relations depend on the scattering
phase shift, and are in general fulfilled only approximately even in the clean
limit, due to the energy dependence of the quasiparticle relaxation time.Comment: 5 pages, 2 Postscript figure
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