186 research outputs found
On the low temperature properties and specific anisotropy of pure anisotropically paired superconductors
Dependences of low temperature behavior and anisotropy of various physical
quantities for pure unconventional superconductors upon a particular form of
momentum direction dependence for the superconducting order parameter (within
the framework of the same symmetry type of superconducting pairing) are
considered. A special attention is drawn to the possibility of different
multiplicities of the nodes of the order parameter under their fixed positions
on the Fermi surface, which are governed by symmetry. The problem of an
unambiguous identification of a type of superconducting pairing on the basis of
corresponding experimental results is discussed. Quasiparticle density of
states at low energy for both homogeneous and mixed states, the low temperature
dependences of the specific heat, penetration depth and thermal conductivity,
the I-V curves of SS and NS tunnel junctions at low voltages are examined. A
specific anisotropy of the boundary conditions for unconventional
superconducting order parameter near for the case of specular reflection
from the boundary is also investigated.Comment: 20 page
Theory of Thermal Conductivity in YBa_2Cu_3O_{7-\delta}
We calculate the electronic thermal conductivity in a d-wave superconductor,
including both the effect of impurity scattering and inelastic scattering by
antiferromagnetic spin fluctuations. We analyze existing experiments,
particularly with regard to the question of the relative importance of
electronic and phononic contributions to the heat current, and to the influence
of disorder on low-temperature properties. We find that phonons dominate heat
transport near T_c, but that electrons are responsible for most of the peak
observed in clean samples, in agreement with a recent analysis of Krishana et
al. In agreement with recent data on YBa_2(Cu_1-xZn_x)_3O_7-\delta the peak
position is found to vary nonmonotonically with disorder.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let
Nonmonotonous Magnetic Field Dependence and Scaling of the Thermal Conductivity for Superconductors with Nodes of the Order Parameter
We show that there is a new mechanism for nonmonotonous behavior of magnetic
field dependence of the electronic thermal conductivity of clean
superconductors with nodes of the order parameter on the Fermi surface. In
particular, for unitary scatterers the nonmonotony of relaxation time takes
place. Contribution from the intervortex space turns out to be essential for
this effect even at low temperatures. Our results are in a qualitative
agreement with recent experimental data for superconducting UPt_3. For
E_{2u}-type of pairing we find approximately the scaling of the thermal
conductivity in clean limit with a single parameter x=T/T_c\sqrt{B_{c2}/B} at
low fields and low temperatures, as well as weak low-temperature dependence of
the anisotropy ratio K_{zz}/K_{yy} in zero field. For E_{1g}-type of pairing
deviations from the scaling are more noticeable and the anisotropy ratio is
essentially temperature dependent.Comment: 37 pages, 8 Postscript figures, REVTE
Heat Transport and the Nature of the Order Parameter in Superconducting
Recent thermal conductivity data on the heavy fermion superconductor
have been interpreted as offering support for an model of the order
parameter as opposed to an model. In this paper, we analyze this issue
from a theoretical standpoint including the detailed effects of Fermi surface
and gap anisotropy. Our conclusion is that although current data put strong
constraints on the gap anisotropy, they cannot definitively distinguish between
these two models. Measurements on samples of varying quality could be decisive
in this regard, however.Comment: 8 pages, revtex, 15 uunencoded postscript figure
Electron-Phonon Interaction and Ultrasonic Attenuation in the Ruthenate and Cuprate superconductors
This article derives an electron-phonon interaction suitable for interpreting
ultrasonic attenuation measurements in the ruthenate and cuprate
superconductors. The huge anisotropy found experimentally (Lupien et al., 2001)
in Sr2RuO4 in the normal state is accounted for in terms of the layered
square-lattice structure of Sr2RuO4, and the dominant contribution to the
attenuation in Sr2RuO4 is found to be due to electrons in the gamma band. The
experimental data in the superconducting state is found to be inconsistent with
vertical lines nodes in the gap in either (100) or (110) planes. Also, a
general method, based on the use of symmetry, is developed to allow for the
analysis of ultrasonic attenuation experiments in superconductors in which the
electronic band structure is complicated or not known. Our results, both for
the normal-state anisotropy, and relating to the positions of the gap nodes in
the superconducting state, are different from those obtained from analyses
using a more traditional model for the electron-phonon interaction in terms of
an isotropic electron stress tensor. Also, a brief discussion of the ultrasonic
attenuation in UPt3 is given.Comment: 12 pages. Comments have been added to the original version of this
article showing how, for the ultrasonic attenuation for a hexagonal crystal
(which must be isotropic with respect to rotations about the c axis) our
approach reproduces the results of the traditional isotropic electron stress
tensor mode
d-Wave Model for Microwave Response of High-Tc Superconductors
We develop a simple theory of the electromagnetic response of a d- wave
superconductor in the presence of potential scatterers of arbitrary s-wave
scattering strength and inelastic scattering by antiferromagnetic spin
fluctuations. In the clean London limit, the conductivity of such a system may
be expressed in "Drude" form, in terms of a frequency-averaged relaxation time.
We compare predictions of the theory with recent data on YBCO and BSSCO
crystals and on YBCO films. While fits to penetration depth measurements are
promising, the low temperature behavior of the measured microwave conductivity
appears to be in disagreement with our results. We discuss implications for
d-wave pairing scenarios in the cuprate superconductors.Comment: 33 pages, plain TeX including all macros. 16 uuencoded, compressed
postscript figures are appended at the en
Possible anomalous Doppler shift effect in superconductor SrRuO
The effect of the Doppler shift is studied in a model for the
- bands of SrRuO consisting of two hybridized 1D bands.
Assuming a superconducting gap with nodes in the diagonal directions, we
examine the oscillation of the surface density of states and the thermal
conductivity under a rotating magnetic field. Upon varying the strength of the
hybridization, the oscillation in these quantities is found to exhibit 2D to 1D
crossover. In the crossover regime, which corresponds to the actual
SrRuO, the thermal conductivity exhibits a two-fold-symmetry
oscillation, while the four-fold-symmetry component in the oscillation is
barely detectable
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