Evolution of the Density of States Gap in a Disordered Superconductor

Abstract

We determine the effect of a random potential on the density of states $N\left(\omega \right)$ in the attractive Hubbard model. At weak coupling, disorder closes the gap concurrently with the destruction of superconductivity. At larger, but still intermediate coupling, a pseudogap in $N\left(\omega \right)$ remains beyond the point at which off-diagonal long range order vanishes. This change in the elementary excitations of the insulating phase corresponds to a crossover between Fermi and Bose insulators.