Magnetic groundstates in a correlated two orbital Hubbard model

TL;DR

This paper investigates the magnetic and orbital phases of a two orbital Hubbard model using dynamical mean field theory, revealing complex magnetic states, a metal-insulator transition at quarter filling, and the importance of Hund's coupling.

Contribution

It provides a detailed analysis of magnetic and orbital orderings in a two orbital Hubbard model, highlighting the role of Hund's coupling and the nature of the metal-insulator transition at quarter filling.

Findings

Discovery of ferromagnetic and antiferromagnetic phases.

Identification of a first-order metal-insulator transition at quarter filling.

Demonstration of the influence of Hund's coupling on magnetic stability.

Abstract

We examine the orbital and magnetic order of the two orbital Hubbard model within dynamical mean field theory. The model describes the low energy physics of a partially filled $e_g$-band as can be found in some transition metal compounds. The model shows antiferromagnetic as well as ferromagnetic phases. For stabilizing ferromagnetism we find that Hund's coupling is particularly important. Quarter filling represents a very special situation in the phase diagram, where the coupling of spin, charge, and orbital degrees of freedom are involved. Exactly at quarter filling we find a metal insulator transition (MIT) between two almost fully polarized ferromagnetic states. This MIT can be tuned by changing the local interaction strength and seems to be a first order transition at zero temperature. Apart from these ferromagnetic states we were also able to stabilize antiferromagnetic and charge ordered phases at quarter filling, depending on the interaction parameters.