From Mott insulator to band insulator: A dynamical mean-field theory study

The question if a Mott insulator and a band insulator are fundamentally different has been the matter of intensive research recently. Here we consider a simple model which allows by tuning one parameter to go continously from a Mott insulator to band insulator. The model consists of two Hubbard systems connected by single particle hopping. The Hubbard Hamiltonian is solved by the Dynamical Mean-Field theory using Quantum Monte Carlo to solve the resulting quantum impurity problem. The quasiparticle spectral function is calculated. Here we focus on the optical conductivity and in particular on the Drude weight which can be experimentally measured. From our calculation we conclude that there is a continous crossover from the band insulator to the Mott insulator phase at finite temperature.