Orbital Order, Metal Insulator Transition, and Magnetoresistance-Effect in the two-orbital Hubbard model

TL;DR

This study investigates how temperature and magnetic field influence a two-orbital Hubbard model at quarter filling, revealing complex phase behavior including orbital order, ferromagnetism, and magnetoresistance effects.

Contribution

It provides a detailed phase diagram of the model, highlighting the interplay of orbital order and ferromagnetism, and uncovers magnetoresistance phenomena near phase transitions.

Findings

Strong magnetoresistance near orbital ferromagnetic transition

Crossover from paramagnetic insulator to metal with increasing Hund's coupling

Rich phase diagram with multiple order mechanisms

Abstract

We study the effects of temperature and magnetic field on a two-orbital Hubbard model within dynamical mean field theory. We focus on the quarter filled system, which is a special point in the phase diagram due to orbital degeneracy. At this particular filling the model exhibits two different long-range order mechanisms, namely orbital order and ferromagnetism. Both can cooperate but do not rely on each other's presence, creating a rich phase diagram. Particularly, in the vicinity of the phase transition to an orbitally ordered ferromagnetic state, we observe a strong magnetoresistance effect. Besides the low temperature phase transitions, we also observe a crossover between a paramagnetic insulating and a paramagnetic metallic state for increasing Hund's coupling at high temperatures.