450 research outputs found
Microwave conductivity in the ferropnictides with specific application to BaKFeAs
We calculate the microwave conductivity of a two band superconductor with
gap symmetry. Inelastic scattering is included approximately in a BCS
model augmented by a temperature dependent quasiparticle scattering rate
assumed, however, to be frequency independent. The possibility that the s-wave
gap on one or the other of the electron or hole pockets is anisotropic is
explored including cases with and without gap nodes on the Fermi surface. A
comparison of our BCS results with those obtained in the Two Fluid Model (TFM)
is provided as well as with the case of the cuprates where the gap has d-wave
symmetry and with experimental results in BaKFeAs. The
presently available microwave conductivity data in this material provides
strong evidence for large anisotropies in the electron pocket s-wave gap. While
a best fit favors a gap with nodes on the Fermi surface this disagrees with
some but not all penetration depth measurements which would favor a node-less
gap as do also thermal conductivity and nuclear magnetic resonance data.Comment: 12 pages, 9 figures. Phys. Rev. B (submitted
Optical conductivity in non-equilibrium d-wave superconductors
We consider the optical conductivity of a d-wave BCS superconductor in the
presence of a non-equilibrium distribution of excess quasiparticles. Two
different simplified models used in the past for the s-wave case are considered
and results compared. In the -model of Parker the excess quasiparticles
are assumed to be in a thermal distribution at some temperature larger
than the equilibrium sample temperature. In the - model of Owen and
Scalapino a chemical potential is introduced to accommodate the excess
quasiparticles. Some of the results obtained are specific to the model, most
are qualitatively similar in both.Comment: 11 pages, 6 figures this manuscript has been accepted for publication
in abbreviated form by Physical Review
Sum rule for the optical scattering rates
An important quantity in electronic systems is the quasiparticle scattering
rate (QPSR). A related optical scattering rate (OSR) is routinely extracted
from optical data, and, while it is not the same as the QPSR, it nevertheless
displays many of the same features. We consider a sum rule which applies to the
area under a closely related quantity, almost equal to the OSR in the low
energy region. We focus on the readjustment caused by, for example, a
quasiparticle density of states change due to the superconducting transition.
Unfortunately, no general statement about mechanism can be made solely on the
energy scale in which the spectral weight readjustment on the OSR occurs.Comment: 22 pages, 7 figures accepted for publication by Phys. Rev.
Microwave conductivity of YBaCuO including inelastic scattering
The fluctuation spectrum responsible for the inelastic scattering in
YBaCuO which was recently determined from consideration of the
in-plane optical conductivity in the infrared, is used to calculate the
temperature dependence of the microwave conductivity at several measured
frequencies. Reasonable overall agreement can only be achieved if, in addition,
some impurity scattering is included within a model potential intermediate
between weak (Born) and strong (unitary) limit.Comment: 15 pages, 5 figures accepted for publication in Phys. Rev.
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