1,659 research outputs found
Transport Properties of "Extended-s" State Superconductors
Superconducting states with "extended s-wave" symmetry have been suggested in
connection with recent ARPES experiments on BSCCO. In the presence of
impurities, thermodynamic properties of such states reflect a residual density
of states for a range of concentrations. While properties reflecting
alone will be similar to those of d-wave states, transport
measurements may be shown to qualitatively distinguish between the two. In
contrast to the d-wave case with unitarity limit scattering, limiting
low-temperature residual conductivities in the s-wave state are large and scale
inversely with impurity concentration.Comment: 4 pages, 5 figures, uuencoded compressed postscript fil
Lower Bound for the Fermi Level Density of States of a Disordered D-Wave Superconductor in Two Dimensions
We consider a disordered d--wave superconductor in two dimensions. Recently,
we have shown in an exact calculation that for a lattice model with a
Lorentzian distributed random chemical potential the quasiparticle density of
states at the Fermi level is nonzero. As the exact result holds only for the
special choice of the Lorentzian, we employ different methods to show that for
a large class of distributions, including the Gaussian distribution, one can
establish a nonzero lower bound for the Fermi level density of states. The fact
that the tails of the distributions are unimportant in deriving the lower bound
shows that the exact result obtained before is generic.Comment: 15 preprint pages, no figures, submitted to PR
Scattering by impurity-induced order parameter ``holes'' in d-wave superconductors
Nonmagnetic impurities in d-wave superconductors cause strong local
suppressions of the order parameter. We investigate the observable effects of
the scatterigng off such suppressions in bulk samples by treating the order
parameter "hole" as a pointlike off-diagonal scatterer treated within a
self-consistent t-matrix approximation. Strong scattering potentials lead to a
finite-energy spectral feature in the d-wave "impurity band", the observable
effects of which include enhanced low-temperature microwave power absorption
and a stronger sensitivity of the London penetration depth to disorder than
found previously in simpler ``dirty'' d-wave models.Comment: 5 pp. Revtex including 4 postscript figures, submitted to Phys. Rev.
Mermin's Pentagram as an Ovoid of PG(3,2)
Mermin's pentagram, a specific set of ten three-qubit observables arranged in
quadruples of pairwise commuting ones into five edges of a pentagram and used
to provide a very simple proof of the Kochen-Specker theorem, is shown to be
isomorphic to an ovoid (elliptic quadric) of the three-dimensional projective
space of order two, PG(3,2). This demonstration employs properties of the real
three-qubit Pauli group embodied in the geometry of the symplectic polar space
W(5,2) and rests on the facts that: 1) the four observables/operators on any of
the five edges of the pentagram can be viewed as points of an affine plane of
order two, 2) all the ten observables lie on a hyperbolic quadric of the
five-dimensional projective space of order two, PG(5,2), and 3) that the points
of this quadric are in a well-known bijective correspondence with the lines of
PG(3,2).Comment: 5 pages, 4 figure
Role of the impurity-potential range in disordered d-wave superconductors
We analyze how the range of disorder affects the localization properties of
quasiparticles in a two-dimensional d-wave superconductor within the standard
non-linear sigma-model approach to disordered systems. We show that for purely
long-range disorder, which only induces intra-node scattering processes, the
approach is free from the ambiguities which often beset the disordered
Dirac-fermion theories, and gives rise to a Wess-Zumino-Novikov-Witten action
leading to vanishing density of states and finite conductivities. We also study
the crossover induced by internode scattering due to a short range component of
the disorder, thus providing a coherent non-linear sigma-model description in
agreement with all the various findings of different approaches.Comment: 38 pages, 1 figur
Anisotropic Optical Conductivity of Nd2-xCexCuO4 Thin Films
Opticcal conductivity spectra of Nd2-xCexCuO4 thin films,
measured by the reflectance-transmittance method (R-T method) which has been
proposed to investigate far-infrared spectroscopy, are investigated based on
the anisotropic pairing model. Precise measurements of the frequency-dependent
conductivity enable us to examine quantitatively the nature of the
superconducting gap through infrared properties in the electron-doped high-Tc
superconductors. We show that the behavior of optical conductivity
is consistent with the anisotropic superconducting gap and is well explained by
the formula for d-wave pairing in the low-energy regime of the far-infrared
region. Our results suggest that the electron-doped cuprate superconductors
Nd2-xCexCuO4 have nodes in the superconducting gap.Comment: 4 pages, 3 figure
- …