METAL-INSULATOR CROSSOVER IN THE BOSON-FERMION MODEL IN INFINITE DIMENSIONS

The boson-fermion model, describing a mixture of tightly bound electro n pairs and quasifree electrons hybridized with each other via a charg e exchange term, is studied in the limit of infinite dimensions using the noncrossing approximation within the dynamical mean field theory. It is shown that a metal-insulator crossover, driven by strong pair fl uctuations, takes place as the temperature is lowered. It manifests it self in the opening of a pseudogap in the electron density of states, accompanied by a corresponding effect in the optical and the de conduc tivity. [S0031-9007(98)07175-0].