Emergent nematicity and intrinsic versus extrinsic electronic scattering processes in the kagome metal CsV3Sb5

Abstract

Fermi-surface fluctuations and lattice instabilities in the two-dimensional metallic kagome superconductor CsV3Sb5 are elucidated via polarization-resolved Raman spectroscopy. The presence of a weak electronic continuum in high-quality samples marks the crossover 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 TCDW, with emergent C2 symmetry for one of the CDW amplitude modes, alluding to nematicity. In conjunction with symmetry-breaking lattice distortions, a kinklike hardening of the A1g phonon energy at TCDW signifies a concerted interplay of electronic correlations and electron-phonon coupling in the exotic CDW order.