SuperconductingTcenhancement due to excitonic negative-Ucenters: A Monte Carlo study

The enhancement of superconductivity by a small concentration of excitonic negative-U centers is studied by a new method which combines diagrammatic perturbation theory and Monte Carlo simulation. Results are given which show how the impurity parameters should be selected in order to obtain the maximum increase in the superconducting transition temperature ${\mathrm{T}}_{\mathrm{c}}$.