Metal-insulator transition in the three-dimensional Hubbard model

Abstract

Recently, unconventional and contradictory behaviors have been reported in the photoemission and optical conductivity experiments on CaVO 3, which lies close to the Mott-type metal-insulator transition. In the optical conductivity experiment, we can see a significant Drude component, indicating that the material is metallic. On the other hand, in the photoemission experiment, there is no significant intensity on E F, which indicates that this material is semiconducting. We study, by using the quantum Monte Carlo simulation, how the gap is developed in the density of state (DOS) and optical conductivity by the Mott transition, in terms of the 3-D half-filled Hubbard model. It is shown that the DOS has a coherent peak just on the Fermi level in the high-temperature region. However, it moves to the high-binding-energy side when the temperature is lowered. The DOS just on the Fermi level is decreased as the decrease of the temperature and eventually, the gap opens in the DOS. The Drude component in the optical conductivity is also decreased with the temperature, but it can remain relatively large compared to the DOS at the Fermi level. We show that the experimentally observed photoemission and optical conductivity spectra of CaVO 3 are described within the present theoretical framework.