# The Nematic Energy Scale and the Missing Electron Pocket in FeSe

## TL;DR

This study uses angle-resolved photoemission spectroscopy to analyze the electronic structure of fully detwinned FeSe across the nematic phase transition, revealing a significant nematic energy scale and clarifying the fate of the electron pocket.

## Contribution

It provides detailed experimental insights into the nematic energy scale and orbital reconstruction in FeSe, aiding the development of theoretical models for superconductivity.

## Key findings

- Nematicity causes a band reconstruction involving dxz, dyz, and dxy orbitals.
- The nematic energy scale between dxz and dyz bands reaches 50 meV.
- The dxz electron pocket is absent in the nematic state, explained by the data.

## Abstract

Superconductivity emerges in proximity to a nematic phase in most iron-based superconductors. It is therefore important to understand the impact of nematicity on the electronic structure. Orbital assignment and tracking across the nematic phase transition prove to be challenging due to the multiband nature of iron-based superconductors and twinning effects. Here, we report a detailed study of the electronic structure of fully detwinned FeSe across the nematic phase transition using angle-resolved photoemission spectroscopy. We clearly observe a nematicity-driven band reconstruction involving dxz, dyz, and dxy orbitals. The nematic energy scale between dxz and dyz bands reaches a maximum of 50 meV at the Brillouin zone corner. We are also able to track the dxz electron pocket across the nematic transition and explain its absence in the nematic state. Our comprehensive data of the electronic structure provide an accurate basis for theoretical models of the superconducting pairing in FeSe.