A General Mechanism for Orbital Selective Phase Transitions

TL;DR

This paper proposes a universal mechanism for orbital selective phase transitions in multi-orbital systems, demonstrating their occurrence under various conditions and relevance to materials like iron pnictides.

Contribution

It introduces a general mean-field mechanism for OSPT that occurs without crystal field splitting or bandwidth differences, applicable to many materials.

Findings

OSPT exists at and near half filling without crystal field splitting.

Heavy doping favors collinear antiferromagnetic states over OSPT.

OSPT is insensitive to Hund's rule coupling strength.

Abstract

Based on the analysis of a two-orbital Hubbard model within a mean-field approach, we propose a mechanism for an orbital selective phase transition (OSPT) where coexistence of localized and itinerant electrons can be realized. We show that this OSPT exists both at and near half filling even in the absence of crystal field splittings or when bandwidths, orbital degeneracies and magnetic states are equal for both orbitals provided the orbitals have different band dispersions. Such conditions should be generally satisfied in many materials. We find that this OSPT is not sensitive to the strength of Hund's rule coupling and that heavy doping favors the collinear antiferromagnetic state over the OSPT. We discuss our results in relation to the iron pnictides.