Orbital ordering in e_g orbital systems: Ground states and thermodynamics of the 120 degree model

TL;DR

This paper investigates the orbital ordering phenomena in e_g orbital systems using the 120 degree model, revealing proximity to multiple phase transitions and characterizing the thermal behavior of competing phases through simulations and theoretical analysis.

Contribution

It provides a detailed analysis of the classical and quantum limits of the 120 degree model, identifying nearby phase transitions and characterizing orbital order and thermal transitions.

Findings

Proximity to several T=0 phase transitions.

Identification of competing ordered phases.

Characterization of thermal phase transitions.

Abstract

Orbital degrees of freedom shape many of the properties of a wide class of Mott insulating, transition metal oxides with partially filled 3d-shells. Here we study orbital ordering transitions in systems where a single electron occupies the e_g orbital doublet and the spatially highly anisotropic orbital interactions can be captured by an orbital-only model, often called the 120 degree model. Our analysis of both the classical and quantum limits of this model in an extended parameter space shows that the 120 degree model is in close proximity to several T=0 phase transitions and various competing ordered phases. We characterize the orbital order of these nearby phases and their associated thermal phase transitions by extensive numerical simulations and perturbative arguments.