16 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
Upper critical field pecularities of superconducting YNi2B2C and LuNi2B2C
We present new upper critical field Hc2(T) data in a broad temperature region
from 0.3K to Tc for LuNi2B2C and YNi2B2C single crystals with well
characterized low impurity scattering rates. The absolute values for all T, in
particular Hc2(0), and the sizeable positive curvature (PC) of Hc2(T) at high
and intermediate T are explained quantitatively within an effective two-band
model. The failure of the isotropic single band approach is discussed in
detail. Supported by de Haas van Alphen data, the superconductivity reveals
direct insight into details of the electronic structure. The observed maximal
PC near Tc gives strong evidence for clean limit type II superconductors.Comment: 4 pages, 2 figures, Phys. Rev. Lett. accepte
Fermi-Liquid Interactions in d-Wave Superconductor
This article develops a quantitative quasiparticle model of the
low-temperature properties of d-wave superconductors which incorporates both
Fermi-liquid effects and band-structure effects. The Fermi-liquid interaction
effects are found to be classifiable into strong and negligible renormalizaton
effects, for symmetric and antisymmetric combinations of the energies of
and quasiparticles, respectively. A particularly
important conclusion is that the leading clean-limit temperature-dependent
correction to the superfluid density is not renormalized by Fermi-liquid
interactions, but is subject to a Fermi velocity (or mass) renormalization
effect. This leads to difficulties in accounting for the penetration depth
measurements with physically acceptable parameters, and hence reopens the
question of the quantitative validity of the quasiparticle picture.Comment: 4 page
Critical temperature and superfluid density suppression in disordered high- cuprate superconductors
We argue that the standard Abrikosov-Gorkov (AG) type theory of in
disordered -wave superconductors breaks down in short coherence length
high- cuprates. Numerical calculations within the Bogoliubov-de Gennes
formalism demonstrate that the correct description of such systems must allow
for the spatial variation of the order parameter, which is strongly suppressed
in the vicinity of impurities but mostly unaffected elsewhere. Suppression of
as measured with respect to the attendant decrease in the superfluid
density is found to be significantly weaker than that predicted by the AG
theory, in good agreement with experiment.Comment: REVTeX, 4 pages, 3 ps figures included [The version to appear in PRB
Sept. 1. Conclusions of the paper unchanged; several changes in text and
figures for added clarity, discussion of phase fluctuations added.
Coherent Potential Approximation for `d - wave' Superconductivity in Disordered Systems
A Coherent Potential Approximation is developed for s-wave and d-wave
superconductivity in disordered systems. We show that the CPA formalism
reproduces the standard pair-breaking formula, the self-consistent Born
Approximation and the self-consistent T-matrix approximation in the appropriate
limits. We implement the theory and compute T_c for s-wave and d-wave pairing
using an attractive nearest neighbor Hubbard model featuring both binary alloy
disorder and a uniform distribution of scattering site potentials. We determine
the density of states and examine its consequences for low temperature heat
capacity. We find that our results are in qualitative agreement with
measurements on Zn doped YBCO superconductors.Comment: 35 pages, 23 figures, submitted to Phys Rev.
The Nonlinear Meissner Effect in Unconventional Superconductors
We examine the long-wavelength current response in anisotropic
superconductors and show how the field-dependence of the Meissner penetration
length can be used to detect the structure of the order parameter. Nodes in the
excitation gap lead to a nonlinear current-velocity constitutive equation at
low temperatures which is distinct for each symmetry class of the order
parameter. The effective Meissner penetration length is linear in and
exhibits a characteristic anisotropy for fields in the -plane that is
determined by the positions of the nodes in momentum space. The nonlinear
current-velocity relation also leads to an intrinsic magnetic torque for
in-plane fields that are not parallel to a nodal or antinodal direction. The
torque scales as for and has a characteristic angular
dependence. We analyze the effects of thermal excitations, impurity scattering
and geometry on the current response of a superconductor, and
discuss our results in light of recent measurements of the low-temperature
penetration length and in-plane magnetization of single-crystals of
and .Comment: 30 pages, RevTeX file with 16 postscript figures. Submitted to Phys.
Rev.
Free Energy and Magnetic Penetration Depth of a -Wave Superconductor in the Meissner State
We investigate the free energy and the penetration depth of a
quasi-two-dimensional d-wave superconductor in the presence of a weak magnetic
field by taking account of thermal, nonlocal and nonlinear effects. In an
approximation in which the superfluid velocity is assumed to be slowly
varying, the free energy is calculated and compared with available results in
several limiting cases. It is shown that either nonlocal or nonlinear effects
may cut off the linear- dependence of both the free energy and the
penetration depth in all the experimental geometries. At extremely low , the
nonlocal effects will also generically modify the linear dependence of the
penetration depth ("nonlinear Meissner effect") in most experimental
geometries, but for supercurrents oriented along the nodal directions, the
effect may be recovered. We compare our predictions with existing experiments
on the cuprate superconductors.Comment: 18 revtex pages with 4 eps figures, final versio
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SASSYS-1 LMFBR systems analysis code
The SASSYS-1 LMFBR systems analysis code has been developed to analyze the consequences of failures in the shutdown heat removal system and to determine whether this system can perform its mission adequately even with some of its components inoperable. The code is especially intended for analyzing the coolability of the reactor core in cases involving natural circulation flows at decay heat power levels. In addition, the code is also capable of analyzing a wide range of transients, from mild operational transients through more severe transients leading to sodium boiling in the core and possible melting of clad and fuel
A comparison of one-dimensional critical mass computations with experiments for completely reflected reactors /
"Date issued: Mar 16, 1956."Operated by Union Carbide and Carbon CorporationMode of access: Internet
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Status and validation of the SAS4A accident-analysis code system
The SAS4A code system is a new tool for analyzing the initial phase of Hypothetical Core Disruptive Accidents (HCDAs) up to gross melting or failures of the subassembly walls. The objective in the development of SAS4A is to provide improved analytical models which represent experimentally demonstrated modes of material response in such accident scenarios. This paper discusses recent improvements in the phenomenological models, gives examples of verification and validation efforts that have been conducted, and illustrates the whole core-analysis implications of using this refined modeling capability