Dynamical cluster approximation study of the anisotropic two-orbital Hubbard model

TL;DR

This study uses the dynamical cluster approximation with quantum Monte Carlo to analyze how short-range fluctuations influence metal-insulator and orbital-selective Mott transitions in a two-orbital Hubbard model with unequal bandwidths.

Contribution

It provides new insights into the phase diagram of the model, revealing the absence of OSMT at small clusters and its emergence at larger clusters due to spatial fluctuations.

Findings

No OSMT at cluster size N_c=2, with a band insulator state at low temperatures.

At N_c=4, five different phases emerge, including an OSMT phase.

Short-range spatial fluctuations significantly affect the nature of the metal-insulator transition.

Abstract

We investigate the properties of a two-orbital Hubbard model with unequal bandwidths on the square lattice in the framework of the dynamical cluster approximation (DCA) combined with a continuous-time quantum Monte Carlo (CT QMC) algorithm. We explore the effect of short-range spatial fluctuations on the nature of the metal-insulator transition and the possible occurrence of an orbital-selective Mott transition (OSMT), as a function of cluster size $N_c$. We observe that for $N_c=2$ no OSMT is present, instead a band insulator state for both orbitals is stabilized at low temperatures due to the appearance of an artificial local ordered state. For $N_c=4$ the DCA calculations suggest the presence of five different phases which originate out of the cooperation and competition between spatial fluctuations and orbitals of different bandwidths and a OSMT phase is stabilized. Based on our results, we discuss the nature of the gap opening.