Disorder effects in BCS-BEC crossover region of attractive Hubbard model
E. Z. Kuchinskii+, N. A. Kuleeva+, M. V. Sadovskii+*
+Institute for Electrophysics UB of the RAS, 620016 Ekaterinburg, Russia
*Institute for Metal Physics UB of the RAS, 620990 Ekaterinburg, Russia
Abstract
We study the disorder effects upon superconducting transition
temperature Tc and the number of local pairs in attractive Hubbard
model within the
combined Nozieres-Schmitt-Rink and DMFT+Σ approximations.
We analyze the wide range of attractive interaction U, from the weak
coupling
region, where instability of the normal phase and superconductivity are well
described by BCS model, to the limit of strong coupling, where
superconducting
transition is determined by Bose-Einstein condensation of compact Cooper
pairs,
forming at temperatures much higher than superconducting transition
temperature.
It is shown that disorder can either suppress Tc in the weak coupling
limit, or
significantly enhance Tc in the case of strong coupling. However, in all
cases we actually prove the validity of generalized Anderson theorem, so that
all changes of Tc are related to change of the effective bandwidth due
to disorder. Similarly, disorder effects on the number of local pairs are
only
due to these band-widening effects.