Pair Hopping Interaction Research Articles

η-PAIRING SUPERCONDUCTIVITY IN THE NEGATIVE-U HUBBARD MODEL: EFFECT OF FLUCTUATIONS AND DISORDER

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 η-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 the introduction of disorder and allowance for finite U are also calculated. Besides the singularities already present in the O(2) nonlinear σ-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 η-pairing phase near the band edges.

CLUSTER EXPANSION AND PAIRING IN A TWO-BAND MODEL OF Cu OXIDES

A two-band model for the high-T c Cu oxide superconductors involving Cu - O exchange and pair-hopping interactions is considered. A cluster expansion for treating fluctuations around a superconducting mean-field background is developed, and shown to converge at T=0 for small but non-zero doping concentration, and small "J/t" couplings.