Abstract
It is shown that a metal–insulator transition can occur far from half-filling in thenegative-U Hubbard model in the presence of long-range repulsive interactions.Specifically, we consider the bcc lattice at an electron concentration of2/3 and show that a CDW insulating state exists which is energetically favoured over therelevant metallic states. The repulsive interaction plays the same role as it does instabilizing a Wigner crystal. Despite the absence of Fermi surface nesting, the CDWinsulator appears at rather small values of the interaction, preceded by a CDWsemimetal at even smaller values. This places severe restrictions on the region ofthe parameter space where superconductivity may exist. We believe that themodel will show similar behaviour for other electron densities and other lattices.
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