Orbital Nematic Order and Interplay with Magnetism in the Two-Orbital Hubbard Model

TL;DR

This study investigates orbital nematic order and its interaction with magnetism in the two-orbital Hubbard model, revealing conditions under which orbital nematicity can exist without magnetic order, relevant to iron-based superconductors.

Contribution

It combines RPA and VCA methods to show how doping influences orbital and magnetic orders, highlighting a regime where orbital nematicity exists independently of magnetism.

Findings

Hole doping suppresses both magnetism and orbital order.

Electron doping suppresses magnetism faster than orbital order.

Orbital nematicity can be stabilized without long-range magnetic order.

Abstract

Motivated by the recent angle-resolved photoemission spectroscopy (ARPES) on FeSe and iron pnictide families of iron-based superconductors, we have studied the orbital nematic order and its interplay with antiferromagnetism within the two-orbital Hubbard model. We used random phase approximation (RPA) to calculate the dependence of the orbital and magnetic susceptibilities on the strength of interactions and electron density (doping). To account for strong electron correlations not captured by RPA, we further employed non-perturbative variational cluster approximation (VCA) capable of capturing symmetry broken magnetic and orbitally ordered phases. Both approaches show that the electron and hole doping affect the two orders differently. While hole doping tends to suppress both magnetism and orbital ordering, the electron doping suppresses magnetism faster. Crucially, we find a realistic parameter regime for moderate electron doping that stabilizes orbital nematicity in the absence of long-range antiferromagnetic order. This is reminiscent of the non-magnetic orbital nematic phase observed recently in FeSe and a number of iron pnictide materials and raises the possibility that at least in some cases, the observed electronic nematicity may be primarily due to orbital rather than magnetic fluctuations.