-pairing
superconductivity in the negative-U
Hubbard model: Effect of fluctuations and disorder,
Int. J. Mod. Phys. B 8 (1994) 2041
J. Stein:
-pairing
superconductivity in the negative-U
Hubbard model: Effect of fluctuations and disorder,
Int. J. Mod. Phys. B 8 (1994) 2041
We have studied the influence of singular fluctuations around the
mean field solution as well as higher order contributions to the
geometry-controlled asymptotic
expansion of the propagators on
-pairing superconductivity in the
strong coupling negative-U Hubbard model in the presence of unpaired
electrons. The modifications of the mean field results due to introduction
of disorder and allowance for finite U are also calculated.
Besides the singularities already present in the O(2) nonlinear
sigma-model we find a
filling depending singular depression of the repulsive effective pair hopping
interaction which strongly alters the mean-field phase diagram and appears to
suppress the -pairing phase
near the band edges.