# Quasi-particle evidence for the nematic state above $T_{\rm{c}}$ in Sr$_x$Bi$_2$Se$_3$

## TL;DR

This study provides bulk quasi-particle evidence of electronic nematicity existing above the superconducting transition in Sr$_x$Bi$_2$Se$_3$, revealing a 2-fold symmetry in specific heat measurements linked to nematic order.

## Contribution

It demonstrates the presence of nematicity in the normal state of Sr$_x$Bi$_2$Se$_3$ using angle-resolved specific heat, highlighting the relation between nematicity and unconventional superconductivity.

## Key findings

- Observation of 2-fold symmetry in specific heat above $T_c$
- Nematicity linked to anisotropic density of states
- Nematic order persists in the normal state

## Abstract

In the electronic nematic state, an electronic system has a lower symmetry than the crystal structure of the same system. Electronic nematic states have been observed in various unconventional superconductors such as cuprate- and iron-based, heavy-fermion, and topological superconductors. The relation between nematicity and superconductivity is a major unsolved problem in condensed matter physics. By angle-resolved specific heat measurements, we report bulk quasi-particle evidence of nematicity in the topological superconductor Sr$_x$Bi$_2$Se$_3$. The specific heat exhibited a clear 2-fold symmetry despite the 6-fold symmetric lattice. Most importantly, the 2-fold symmetry appeared in the normal state above the superconducting transition temperature. This is explained by the angle-dependent Zeeman effect due to the anisotropic density of states in the nematic phase. Such results highlight the interrelation between nematicity and unconventional superconductivity.