Competition between disorder and Coulomb interaction in a two-dimensional plaquette Hubbard model

초록

We have studied a disordered N-c x N-c plaquette Hubbard model on a two-dimensional square lattice at half-filling using a coherent potential approximation (CPA) in combination with a single-site dynamical mean field theory (DMFT) approach with a paramagnetic bath. Such a model conveniently interpolates between the ionic Hubbard model at N-c = root 2 and the Anderson model at N-c = 8 and enables the analysis of the various limiting properties. We confirmed that within the CPA approach a band insulator behavior appears for noninteracting strongly disordered systems with a small plaquette size N-c = 4, while the paramagnetic Anderson insulator with nearly gapless density of states is present for large plaquette sizes N-c = 48. When the interaction U is turned on in the strongly fluctuating random potential regions, the electrons on the low energy states push each other into high energy states in DMFT in a paramagnetic bath and correlated metallic states with a quasiparticle peak and Hubbard bands emerge, though a larger critical interaction U is needed to obtain this state from the paramagnetic Anderson insulator (N-c = 48) than from the band insulator (N-c = 4). Finally, we observe a Mott insulator behavior in the strong interaction U regions for both N-c = 4 and N-c = 48 independent of the disorder strength. We discuss the application of this model to real materials.

키워드