# The key ingredients of the electronic structure of FeSe

## TL;DR

This paper reviews the electronic structure of FeSe, highlighting its unique multi-band, orbitally-dependent correlations, nematic electronic state, and implications for understanding and enhancing its superconductivity.

## Contribution

It provides a comprehensive overview of FeSe's electronic structure, emphasizing the role of nematicity and pressure effects in its superconducting properties.

## Key findings

- FeSe has small Fermi surfaces and strong orbital-dependent correlations.
- The tetragonal-orthorhombic transition induces a nematic electronic state.
- Pressure tuning affects the nematic state and superconductivity.

## Abstract

FeSe is a fascinating superconducting material at the frontier of research in condensed matter physics. Here we provide an overview on the current understanding of the electronic structure of FeSe, focusing in particular on its low energy electronic structure as determined from angular resolved photoemission spectroscopy, quantum oscillations and magnetotransport measurements of single crystal samples. We discuss the unique place of FeSe amongst iron-based superconductors, being a multi-band system exhibiting strong orbitally-dependent electronic correlations and unusually small Fermi surfaces, prone to different electronic instabilities. We pay particular attention to the evolution of the electronic structure which accompanies the tetragonal-orthorhombic structural distortion of the lattice around 90 K, which stabilizes a unique nematic electronic state. Finally, we discuss how the multi-band multi-orbital nematic electronic structure has an impact on the understanding of the superconductivity, and show that the tunability of the nematic state with chemical and physical pressure will help to disentangle the role of different competing interactions relevant for enhancing superconductivity.