Evidence for an odd-parity nematic phase above the charge density wave transition in kagome metal CsV$_3$Sb$_5$

TL;DR

This study provides thermodynamic evidence for an odd-parity nematic phase existing above the charge density wave transition in CsV₃Sb₅, revealing a complex interplay of symmetry-breaking phenomena in this kagome metal.

Contribution

It uncovers an odd-parity nematic state above the CDW transition, distinct from known ferro-orbital nematicity, and suggests the presence of an exotic loop-current order.

Findings

Detection of twofold in-plane magnetic anisotropy below 130 K

Absence of elastoresistance anomalies near 130 K

Observation of a first-order phase transition indicating time-reversal symmetry breaking

Abstract

The quest for fascinating quantum states arising from the interplay between correlation, frustration, and topology is at the forefront of condensed-matter physics. Recently discovered nonmagnetic kagome metals $A$V${_3}$Sb${_5}$ ($A=$ K, Cs, Rb) with charge density wave (CDW) and superconducting instabilities may host such exotic states. Here we report that an odd electronic nematic state emerges above the CDW transition temperature ($T_{\rm CDW}=94$ K) in CsV${_3}$Sb${_5}$. High-resolution torque measurements reveal a distinct twofold in-plane magnetic anisotropy that breaks the crystal rotational symmetry below $T^*\approx130$ K. However, no relevant anomalies are detected in the elastoresistance data near $T^*$, which excludes the even-parity ferro-orbital nematicity often found in other superconductors. Moreover, in the temperature range between $T_{\rm CDW}$ and $T^*$, conical rotations of magnetic field yield a distinct first-order phase transition, indicative of time-reversal symmetry breaking. These results provide thermodynamic evidence for the emergence of an odd-parity nematic order, implying that an exotic loop-current state precedes the CDW in CsV$_3$Sb$_5$.