519 research outputs found
Spin-Hall Conductivity in Electron-Phonon Coupled Systems
We derive the ac spin-Hall conductivity of
two-dimensional spin-orbit coupled systems interacting with dispersionless
phonons of frequency . For the linear Rashba model we show that the
electron-phonon contribution to the spin-vertex corrections breaks the
universality of at low-frequencies and provides a
non-trivial renormalization of the interband resonance. On the contrary, in a
generalized Rashba model for which the spin-vertex contributions are absent,
the coupling to the phonons enters only through the self-energy, leaving the
low frequency behavior of unaffected by the
electron-phonon interaction.Comment: 4 pages, 3 figures, version as printe
Even-Odd and Super-Even Effects in the Attractive Hubbard Model
The canonical BCS wave function is tested for the attractive Hubbard model.
Results are presented for one dimension, and are compared with the exact
solutions by the Bethe ansatz and the results from the conventional grand
canonical BCS approximation, for various chain lengths, electron densities, and
coupling strengths. While the exact ground state energies are reproduced very
well both by the canonical and grand canonical BCS approximations, the
canonical method significantly improves the energy gaps for small systems and
weak coupling. The ``parity'' effect due to the number of electrons being even
or odd naturally emerges in our canonical results. Furthermore, we find a
``super-even'' effect: the energy gap oscillates as a function of even electron
number, depending on whether the number of electrons is or (m
integer). Such oscillations as a function of electron number should be
observable with tunneling measurements in ultrasmall metallic grains.Comment: 20 pages, 9 figure
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
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