Slave-boson theory of the Mott transition in the two-band Hubbard model

TL;DR

This paper uses the slave-boson mean-field approach to study the Mott transition in a two-band Hubbard model with Hund's coupling, revealing conditions for separate or joint band transitions and novel insulating or magnetic states.

Contribution

It applies and extends the slave-boson method to analyze the Mott transition in a two-band model with Hund's coupling and fractional fillings, providing new insights into phase behavior.

Findings

Identification of conditions for separate and joint Mott transitions

Observation of band insulating and ferromagnetic metallic states

Confirmation of previous theoretical aspects through mean-field analysis

Abstract

We apply the slave-boson approach of Kotliar and Ruckenstein to the two-band Hubbard model with an Ising like Hund's rule coupling and bands of different widths. On the mean-field level of this approach we investigate the Mott transition and observe both separate and joint transitions of the two bands depending on the choice of the inter- and intraorbital Coulomb interaction parameters. The mean-field calculations allow for a simple physical interpretation and can confirm several aspects of previous work. Beside the case of two individually half-filled bands we also examine what happens if the original metallic bands possess fractional filling either due to finite doping or due to a crystal field which relatively shifts the atomic energy levels of the two orbitals. For appropriate values of the interaction and of the crystal field we can observe a a band insulating state and a ferromagnetic metal.