Non-local $d_{xy}$ nematicity and the missing electron pocket in FeSe

TL;DR

This paper proposes a model where $d_{xy}$ orbital nematicity explains the Fermi surface and superconducting gap anisotropy in FeSe, predicting a Lifshitz transition influenced by temperature and doping.

Contribution

It introduces a novel scenario incorporating $d_{xy}$ nematicity to explain FeSe's electronic structure and superconducting properties, aligning well with experimental observations.

Findings

The model reproduces the Fermi surface and gap anisotropy in FeSe.

Predicts a Lifshitz transition of an electron pocket with doping and temperature.

Provides constraints on nematic mechanisms in iron-based superconductors.

Abstract

The origin of spontaneous electronic nematic ordering provides important information for understanding iron-based superconductors. Here, we analyze a scenario where the $d_{xy}$ orbital strongly contributes to nematic ordering in FeSe. We show that the addition of $d_{xy}$ nematicity to a pure $d_{xz}/d_{yz}$ order provides a natural explanation for the unusual Fermi surface and correctly reproduces the strongly anisotropic momentum dependence of the superconducting gap. We predict a Lifshitz transition of an electron pocket mediated by temperature and sulphur doping, whose signatures we discuss by analysing available experimental data. We present the variation of momentum dependence of the superconducting gap upon suppression of nematicity. Our quantitatively accurate model yields the transition from tetragonal to nematic FeSe and the FeSe$_{1-x}$S$_{x}$ series, and puts strong constraints on possible nematic mechanisms.