Absence of $E_{2g}$ nematic instability and dominant $A_{1g}$ response in the kagome metal CsV$_3$Sb$_5$

TL;DR

This study uses elastoresistivity measurements to investigate the symmetry-breaking phenomena in CsV$_3$Sb$_5$, finding no evidence of nematic instability below the charge density wave transition, contrary to prior reports.

Contribution

The paper provides the first comprehensive elastoresistivity analysis using multiple techniques, clarifying the absence of nematic fluctuations and identifying the $A_{1g}$ response as dominant.

Findings

No temperature dependence of $m_{E_{2g}}$ except at $T_{CDW}$

Elastocaloric effect shows no nematic susceptibility enhancement

$m_{A_{1g}}$ peaks at 90 near $T^*=20$ K

Abstract

Ever since the discovery of the charge density wave (CDW) transition in the kagome metal CsV$_3$Sb$_5$, the nature of its symmetry breaking is under intense debate. While evidence suggests that the rotational symmetry is already broken at the CDW transition temperature ($T_{\rm CDW}$), an additional electronic nematic instability well below $T_{\rm CDW}$ has been reported based on the diverging elastoresistivity coefficient in the anisotropic channel ($m_{E_{2g}}$). Verifying the existence of a nematic transition below $T_{\rm CDW}$ is not only critical for establishing the correct description of the CDW order parameter, but also important for understanding low-temperature superconductivity. Here, we report elastoresistivity measurements of CsV$_3$Sb$_5$ using three different techniques probing both isotropic and anisotropic symmetry channels. Contrary to previous reports, we find the anisotropic elastoresistivity coefficient $m_{E_{2g}}$ is temperature-independent, except for a step jump at $T_{\rm CDW}$. The absence of nematic fluctuations is further substantiated by measurements of the elastocaloric effect, which show no enhancement associated with nematic susceptibility. On the other hand, the symmetric elastoresistivity coefficient $m_{A_{1g}}$ increases below $T_{\rm CDW}$, reaching a peak value of 90 at $T^* = 20$ K. Our results strongly indicate that the phase transition at $T^*$ is not nematic in nature and the previously reported diverging elastoresistivity is due to the contamination from the $A_{1g}$ channel.