Metal-insulator transition in the presence of excitonic correlation

We study the possibility of an excitonic transition in a two-band model and show that a true phase transition does not occur in the presence of hybridization since the one-body mixing term acts as a the order parameter of the excitonic phase. We suggest an alternative interpretation for recent experiments on rare earth semiconductors based on a metal-insulator transition associated with the opening or closing of a hybridization gap at a critical pressure. (C) 1996 American Institute of Physics.