Berlin 2012 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 50: Superconductivity: (General) Theory
TT 50.2: Vortrag
Freitag, 30. März 2012, 09:45–10:00, H 3010
Reliability study of the Migdal-Eliashberg theory for strong coupling superconductors — Johannes Bauer1, Jong E Han1,2, and •Olle Gunnarsson1 — 1Max-Planck Institute for Solid State Research, Heisenbergstr.1, 70569 Stuttgart, Germany — 2Department of Physics, SUNY at Buffalo, Buffalo, New York 14260, USA
The Migdal-Eliashberg (ME) theory for strong electron-phonon coupling
and retardation effects of the Morel-Anderson type form the basis for
the quantitative understanding of conventional superconductors.
In recent years, the validity of the ME theory for values of the
electron-phonon coupling strength λ>1 has been questioned by
model studies. By distinguishing bare and effective parameters, and by
comparing the ME theory with the dynamical mean field theory (DMFT), we
clarify the range of applicability of the ME theory. Specifically, we
show that ME theory is very accurate as long as the product of
effective parameters, λ ωph/D, where ωph is an
appropriate phonon scale and D an electronic scale, is small enough
[1].
The effectiveness of retardation effects for the competing Coulomb
interaction is usually considered based on the lowest order diagram in
the perturbation theory. We analyze these effects to higher order and
find modifications to the usual result for the Coulomb
pseudo-potential µ*. Retardation effects are weakened due to a
reduced effective bandwidth appearing in the expressions. Comparsion
with the non-perturbative DMFT corroborates our findings [2].
J Bauer, J E Han, and O Gunnarsson, Phys. Rev. B. 84, 184531 (2011).
J Bauer, J E Han, and O Gunnarsson, in preparation (2011).