Charge induced nematicity in FeSe

TL;DR

This paper demonstrates that charge fluctuations drive nematicity in FeSe, revealing a Pomeranchuk instability through symmetry-resolved Raman scattering and linking electronic nematic fluctuations to structural transitions.

Contribution

It provides direct evidence of charge-induced nematicity and identifies a d-wave Pomeranchuk instability as the underlying mechanism in FeSe.

Findings

Critical charge nematic fluctuations observed near T_S

Diverging nematic susceptibility indicates Pomeranchuk instability

Structural distortion driven by charge nematicity

Abstract

The spontaneous appearance of nematicity, a state of matter that breaks rotation but not translation symmetry, is one of the most intriguing property of the iron based superconductors (Fe SC), and has relevance for the cuprates as well. Establishing the critical electronic modes behind nematicity remains however a challenge, because their associated susceptibilities are not easily accessible by conventional probes. Here using FeSe as a model system, and symmetry resolved electronic Raman scattering as a probe, we unravel the presence of critical charge nematic fluctuations near the structural / nematic transition temperature, T$_S\sim$ 90 K. The diverging behavior of the associated nematic susceptibility foretells the presence of a Pomeranchuk instability of the Fermi surface with d-wave symmetry. The excellent scaling between the observed nematic susceptibility and elastic modulus data demonstrates that the structural distortion is driven by this d-wave Pomeranchuk transition. Our results make a strong case for charge induced nematicity in FeSe.