3,569 research outputs found
Fermi-liquid based theory for the in-plane magnetic anisotropy in untwinned high-T superconductors
Using a generalized RPA-type theory we calculate the in-plane anisotropy of
the magnetic excitations in hole-doped high- superconductors. Extending
our earlier Fermi-liquid based studies on the resonance peak by inclusion of
orthorhombicity we still find two-dimensional spin excitations, however, being
strongly anisotropic. This reflects the underlying anisotropy of the hopping
matrix elements and of the resultant superconducting gap function. We compare
our calculations with new experimental data on {\it fully untwinned}
and find good agreement. Our results are in contrast
to earlier interpretations on the in-plane anisotropy in terms of stripes (H.
Mook {\it et al.}, Nature {\bf 404}, 729 (2000)), but reveal a conventional
solution to this important problem.Comment: 5 pages, 6 figure
Theory for ultrafast nonequilibrium dynamics in d-wave superconductors
We use density-matrix theory to calculate the ultrafast dynamics of
unconventional superconductors from a microscopic viewpoint. We calculate the
time evolution of the optical conductivity as well as pump-probe spectra for a
d-wave order parameter. Three regimes can be distinguished in the spectra. The
Drude response at low photon energies is the only one of those which has been
measured experimentally so far. At higher energies, we predict two more
regimes: the pair-breaking peak, which is reduced as Cooper-pairs are broken up
by the exciting pulse; and a suppression above the pair-breaking peak due to
nonequilibrium quasiparticles. Furthermore, we consider the influence of the
electron-phonon coupling, and derive rate equations which have been widely used
so far.Comment: 4 pages, 4 figure
Electronic Raman response in anisotropic metals
Using a generalized response theory we derive the electronic Raman response
function for metals with anisotropic relaxation rates. The calculations account
for the long--range Coulomb interaction and treat the collision operator within
a charge conserving relaxation time approximation. We extend earlier treatments
to finite wavenumbers () and incorporate inelastic
electron--electron scattering besides elastic impurity scattering. Moreover we
generalize the Lindhard density response function to the Raman case. Numerical
results for the quasiparticle scattering rate and the Raman response function
for cuprate superconductors are presented.Comment: 5 pages, 4figures. accepted in PRB (Brief Report), in pres
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