Emergent nematicity and intrinsic vs. extrinsic electronic scattering processes in the kagome metal CsV$_3$Sb$_5$

TL;DR

This study uses polarization-resolved Raman spectroscopy to explore the interplay of electronic scattering, lattice instabilities, and nematicity in the kagome superconductor CsV$_3$Sb$_5$, revealing how impurities and electronic correlations influence charge-density-wave order.

Contribution

It provides new insights into the roles of intrinsic and extrinsic scattering processes and nematicity in the CDW phase of CsV$_3$Sb$_5$, highlighting the interplay between electronic and lattice effects.

Findings

Impurity-rich samples show defect-induced electronic scattering.

Emergence of $C2$ symmetry in CDW amplitude mode indicates nematicity.

Phonon anomalies and energy hardening at $T_{ ext{CDW}}$ reveal electron-phonon coupling.

Abstract

Fermi surface fluctuations and lattice instabilities in the 2D metallic kagome superconductor CsV$_3$Sb$_5$ are elucidated via polarization-resolved Raman spectroscopy. The presence of a weak electronic continuum in high-quality samples marks the cross-over into the charge-density-wave (CDW) ordered phase, while impurity-rich samples promote strong defect-induced electronic scattering processes that affect the coherence of the CDW phase. CDW-induced phonon anomalies appear below $T_{\mathrm{CDW}}$, with emergent $C2$ symmetry for one of the CDW amplitude modes, alluding to nematicity. In conjunction with symmetry-breaking lattice distortions, a kink-like hardening of the A$_{1g}$ phonon energy at $T_{\mathrm{CDW}}$ signifies a concerted interplay of electronic correlations and electron-phonon coupling in the exotic CDW order.