Phase diagram for the exciton Mott transition in infinite-dimensional electron–hole systems

Abstract

To understand the essence of the exciton Mott transition in three-dimensional electron–hole systems, the metal–insulator transition is studied for a two-band Hubbard model in infinite dimensions with interactions of electron–electron (hole–hole) repulsion U and electron–hole attraction - U ′ . By using the dynamical mean-field theory, the phase diagram in the U– U ′ plane is obtained (which is exact in infinite dimensions) assuming that electron–hole pairs do not condense. When both electron and hole bands are half-filled, two types of insulating states appear: the Mott–Hubbard insulator for U > U ′ and the biexciton-like insulator for U < U ′ . Even when away from half-filling, we find the phase transition between the exciton- or biexciton-like insulator and a metallic state. This transition can be assigned to the exciton Mott transition, whereas the Mott–Hubbard transition is absent.