Electronic structure properties in the nematic phases of FeSe

TL;DR

This study analyzes the electronic structures of FeSe in various nematic phases, identifying the d-wave bond nematic order as the key factor explaining experimental observations including band splittings, Dirac cones, and doping effects.

Contribution

It demonstrates that the d-wave bond nematic order, combined with spin-orbit coupling, explains multiple experimental features of FeSe's nematic phase.

Findings

dBN order explains temperature-dependent band splittings

Dirac cones and their T-dependence are consistent with dBN order

Thickness and doping effects are due to electron doping and Se height changes

Abstract

We investigate the electronic structures of FeSe in the presence of different possible orders. We find that only ferro-orbital order (FO) and collinear antiferro-magnetism (C-AFM) can simultaneously induce splittings at $\Gamma$ and M. Bicollinear antiferro-magnetism (B-AFM) and spin-orbit coupling (SOC) have very similar band structure on $\Gamma$-M near the Fermi level. The temperature insensitive splitting at $\Gamma$ and the temperature dependent splitting at M observed in recent experiments can be explained by the d-wave bond nematic (dBN) order together with SOC. The recent observed Dirac cones and their temperature ($T$) dependence in FeSe thin films can also be well explained by the dBN order with band renormalization. Their thickness- and cobalt-doping- dependent behaviors are the consequences of electron doping and reduction of Se height. All these suggest that the nematic order in FeSe system is the dBN order.