796 research outputs found
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
Microwave Conductivity due to Scattering from Extended Linear Defects in d-Wave Superconductors
Recent microwave conductivity measurements of detwinned, high-purity,
slightly overdoped YBaCuO crystals reveal a linear
temperature dependence and a near-Drude lineshape for temperatures between 1
and 20 K and frequencies ranging from 1 to 75 GHz. Prior theoretical work has
shown that simple models of scattering by point defects (impurities) in d-wave
superconductors are inconsistent with these results. It has therefore been
suggested that scattering by extended defects such as twin boundary remnants,
left over from the detwinning process, may also be important. We calculate the
self-energy and microwave conductivity in the self-consistent Born
approximation (including vertex corrections) for a d-wave superconductor in the
presence of scattering from extended linear defects. We find that in the
experimentally relevant limit (), the
resulting microwave conductivity has a linear temperature dependence and a
near-Drude frequency dependence that agrees well with experiment.Comment: 13 pages, 7 figure
Quasiparticles and Phase Fluctuations in High Tc Superconductors
We argue based on theoretical considerations and analysis of experimental
data that quasiparticle excitations near the nodes determine the low
temperature properties in the superconducting state of cuprates. Quantum
effects of phase fluctuations are shown to be quantitatively important, but
thermal effects are small for . An anisotropic superfluid Fermi
liquid phenomenology is presented for the effect of quasiparticle interactions
on the temperature and doping dependence of the low penetration depth.Comment: M2S-HTSC-VI, doping dependence of phase flucns revised, final versio
Anomalous Charge Dynamics in the Superconducting State of Underdoped Cuprates
We present fermi liquid expressions for the low temperature behavior of the
superfluid stiffness, explain why they differ from those suggested recently by
Lee and Wen, and discuss their applicability to data on high-
superconductors. We find that a consistent description requires a strong,
doping dependent anisotropy, which affects states near the zone corners much
more strongly than those near the zone diagonals
Orbital Currents in Underdoped Cuprates
Orbital currents, either fluctuating or static, have emerged as promising
candidates for a description of the pseudogap state in underdoped cuprates. I
shall review the evolution of these ideas and describe some experiments which
have been proposed to test the existence of orbital currents.Comment: 6 pages; Proceedings of the SNS 2001 Conferenc
Low-energy Spectra of the t-J-Type Models Studied by Variational Approach
We discuss recent progress of understanding the phenomena observed in high Tc
cuprates by studying the d-wave resonating-valence-bond (d-RVB) based trial
wave functions for the 2-dimensional t-J-type models. Treat exactly the strong
correlation between electrons by numerical approach, we examine the evolution
of ground states described by different variational wave functions and
properties of the quasi-hole and -particle excitations of the d-RVB
superconducting (SC) state. Properties related to the Fermi surface geometry
deduced from quasi-hole energy dispersion of the SC state is shown to be
consistent with the observation by photoemission spectroscopy. With the
calculated spectral weights (SW's) for adding and removing an electron, we
found not only the anti-correlation between conductance peak height and width
between peaks seen in tunneling experiments, but also unique properties due to
strong correlation which need to be verified by future experiments.Comment: 6 revtex pages with 5 (.eps) figures. To appear in a special volume
of Journal of Magnetism and Magnetic Materials for the ICM 2006 proceeding
Infrared properties of exotic superconductors
The infrared spectra of the non-traditional superconductors share certain
common features. The lack of a gap signature at and the residual
conductivity are the consequence of a d-wave order parameter. The high
materials, the organic conductors and the heavy Fermion materials have a strong
mid-infrared absorption band which can be interpreted as strong coupling of the
carriers to electronic degrees of freedom which leads to a breakdown of the
Fermi liquid picture. The cuprates and the organic charge transfer salts are
unique in possessing an intrinsic low dimensionality. The charge transport
normal to the highly conducting direction is incoherent down to the lowest
temperatures and frequencies.Comment: 10 pages 11 figures, From the proceedings of the First Euroconference
on Anomalous Complex Superconductors, Heraklion, Crete. Sept 1998, to be
published in Physica
Non-quasiparticle microwave absorption in
We show that a non-quasiparticle charge collective mode, in parallel and
coincident with the d-wave pair conductivity, leads to a quantitative
understanding of microwave surface impedance measurements on superconducting
. The analysis suggests an inhomogeneous
charge ground state in and other HTS.Comment: 6 pages, 3 figure
Microwave Spectroscopy of Thermally Excited Quasiparticles in YBa_2Cu_3O_{6.99}
We present here the microwave surface impedance of a high purity crystal of
measured at 5 frequencies between 1 and 75 GHz. This data
set reveals the main features of the conductivity spectrum of the thermally
excited quasiparticles in the superconducting state. Below 20 K there is a
regime of extremely long quasiparticle lifetimes, due to both the collapse of
inelastic scattering below and the very weak impurity scattering in the
high purity -grown crystal used in this study. Above 20 K, the
scattering increases dramatically, initially at least as fast as .Comment: 13 pages with 10 figures. submitted to Phys Rev
- …