# Electronic anisotropies revealed by detwinned ARPES measurements of FeSe

## TL;DR

This study uses detwinned ARPES measurements to reveal the electronic anisotropies in FeSe, showing a single electron pocket in the nematic phase, clarifying previous controversies.

## Contribution

First high-resolution ARPES measurements on detwinned FeSe revealing the true low-temperature Fermi surface structure.

## Key findings

- Only one peanut-shaped electron pocket observed at low temperatures
- Fermi surface consists of one elliptical hole and one orthogonal electron pocket
- Clarifies previous ambiguities in ARPES interpretations of FeSe

## Abstract

We report high resolution ARPES measurements of detwinned FeSe single crystals. The application of a mechanical strain is used to promote the volume fraction of one of the orthorhombic domains in the sample, which we estimate to be 80$\%$ detwinned. While the full structure of the electron pockets consisting of two crossed ellipses may be observed in the tetragonal phase at temperatures above 90~K, we find that remarkably, only one peanut-shaped electron pocket oriented along the longer $a$ axis contributes to the ARPES measurement at low temperatures in the nematic phase, with the expected pocket along $b$ being not observed. Thus the low temperature Fermi surface of FeSe as experimentally determined by ARPES consists of one elliptical hole pocket and one orthogonally-oriented peanut-shaped electron pocket. Our measurements clarify the long-standing controversies over the interpretation of ARPES measurements of FeSe.