Suppression of Mott-Hubbard states and metal-insulator transitions in the two band Hubbard model

TL;DR

This paper explores how additional orbitals in a two-band Hubbard model suppress Mott-Hubbard states and alter metal-insulator transitions, highlighting the importance of multi-band effects in real materials.

Contribution

It demonstrates that multi-band correlations suppress the metal-insulator transition, with orbital ordering affecting the formation of Mott-Hubbard states.

Findings

Additional orbitals increase the critical coupling for the transition.

Orbital ordering hinders Mott-Hubbard states and induces band gaps.

Multi-band correlations may lead to more band insulators than Mott insulators.

Abstract

I investigate band and Mott insulating states in a two-band Hubbard model, with the aim of understanding the differences between the idealised one-orbital model and the more realistic multi-band case. Using a projection ansatz I show that additional orbitals suppress the metal-insulator transition, leading to a critical coupling of approximately eight times the bare band-width. I also demonstrate the effects of orbital ordering, which hinder Mott-Hubbard states and open a band gap. Since multi-band correlations are common in real materials, this work suggests that the existence of very strongly correlated band insulators may be more common than Mott-Hubbard insulators.