21 research outputs found
Impurity scattering and localization in -wave superconductors
Strong evidence is presented for the localization of low energy quasiparticle
states in disordered -wave superconductors. Within the framework of the
Bogoliubov-de Gennes (BdG) theory applied to the extended Hubbard model with a
finite concentration of non-magnetic impurities, we carry out a fully
self-consistent numerical diagonalization of the BdG equations on finite
clusters containing up to sites. Localized states are identified
by probing their sensitivity to the boundary conditions and by analyzing the
finite size dependence of inverse participation ratios.Comment: 4 pages REVTeX with 2 embedded .ps figures; submitted to PRB as Rapid
Communicatio
Polar Kerr Effect as Probe for Time-Reversal Symmetry Breaking in Unconventional Superconductors
The search for broken time reversal symmetry (TRSB) in unconventional
superconductors intensified in the past year as more systems have been
predicted to possess such a state. Following our pioneering study of TRSB
states in SrRuO using magneto-optic probes, we embarked on a systematic
study of several other of these candidate systems. The primary instrument for
our studies is the Sagnac magneto-optic interferometer, which we recently
developed. This instrument can measure magneto-optic Faraday or Kerr effects
with an unprecedented sensitivity of 10 nanoradians at temperatures as low as
100 mK. In this paper we review our recent studies of TRSB in several systems,
emphasizing the study of the pseudogap state of high temperature
superconductors and the inverse proximity effect in superconductor/ferromagnet
proximity structures.Comment: A review pape
Proximity Effect and Josephson Coupling in the SO(5) Theory of High-Tc Superconductivity
We consider proximity effect coupling in
Superconducting/Antiferromagnetic/Superconducting (S-A-S) sandwiches using the
recently developed SO(5) effective theory of high temperature
superconductivity. We find that, for narrow junctions, the A region acts like a
strong superconductor, and that there is a critical junction thickness which
depends on the effective SO(5) coupling constants and on the phase difference
across the junction, at which the A region undergoes a Freedericksz-like
transition to a state which is intermediate between superconductor and
antiferromagnet. For thick junctions, the current-phase relation is sinusoidal,
as in standard S-N-S and S-I-S junctions, but for thin junctions it shows a
sharp break in slope at the Freedericksz point.Comment: 4 pages, LATEX, 5 eps fig
Is Sr2RuO4 a Chiral P-Wave Superconductor?
Much excitement surrounds the possibility that strontium ruthenate exhibits
chiral p-wave superconducting order. Such order would be a solid state analogue
of the A phase of He-3, with the potential for exotic physics relevant to
quantum computing. We take a critical look at the evidence for such
time-reversal symmetry breaking order. The possible superconducting order
parameter symmetries and the evidence for and against chiral p-wave order are
reviewed, with an emphasis on the most recent theoretical predictions and
experimental observations. In particular, attempts to reconcile experimental
observations and theoretical predictions for the spontaneous supercurrents
expected at sample edges and domain walls of a chiral p-wave superconductor and
for the polar Kerr effect, a key signature of broken time-reversal symmetry,
are discussed.Comment: To appear in the proceedings of LT25 (Amsterdam, August 2008
Microwave Conductivity due to Impurity Scattering in a d-wave Superconductor
The self-consistent t-matrix approximation for impurity scattering in
unconventional superconductors is used to interpret recent measurements of the
temperature and frequency dependence of the microwave conductivity of YBCO
crystals below 20K. In this theory, the conductivity is expressed in terms of a
fequency dependent single particle self-energy, determined by the impurity
scattering phase shift which is small for weak (Born) scattering and approaches
for unitary scattering. Inverting this process, microwave
conductivity data are used to extract an effective single-particle self-energy
and obtain insight into the nature of the operative scattering processes. It is
found that the effective self-energy is well approximated by a constant plus a
linear term in frequency with a small positive slope for thermal quasiparticle
energies below 20K. Possible physical origins of this form of self-energy are
discussed.Comment: 5 pages, 4 figure
GINZBURG-LANDAU THEORY OF VORTICES IN -WAVE SUPERCONDUCTORS
Ginzburg-Landau theory is used to study the properties of single vortices and
of the Abrikosov vortex lattice in a superconductor. For a single
vortex, the -wave order parameter has the expected four-lobe structure in a
ring around the core and falls off like at large distances. The
topological structure of the -wave order parameter consists of one
counter-rotating unit vortex, centered at the core, surrounded by four
symmetrically placed positive unit vortices. The Abrikosov lattice is shown to
have a triangular structure close to and an oblique structure at lower
temperatures. Comparison is made to recent neutron scattering data.Comment: 4 pages, REVTeX, 3 figures available upon reques