Interaction-driven Mott Transition with a non-degenerate Ground State in the Orbital Hatsugai-Kohmoto model

Recent work on the Mott transition has focused on the exactly solvable model of Hatsugai/Kohmoto (HK) which is strictly local in momentum space. We explore an extension of this model in which orbital degrees of freedom are incorporated. We find dramatically different behaviour in the interaction-driven Mott transition in this model compared to the band HK model. First, unlike the band HK model in which the interaction must exceed a critical value for the insulating state to obtain, we find an insulating state for all interaction strengths in agreement with state-of-the-art cluster calculations. Second, we find that the density of states deviates strongly from single-site dynamical mean field theory (DMFT) calculations on the Hubbard model (which show the spectral weight at zero frequency contains a coherence quasiparticle peak). We characterize the Mott transition by computing the compressibility, entropy and heat capacity, displaying novel non-Fermi liquid behaviour driven by strong correlations. We conclude that the orbital version of HK offers an exactly solvable model of the Mott problem in agreement with more complex cluster methods but with minimal computational cost.