Emergent nematicity and intrinsic versus extrinsic electronic scattering processes in the kagome metal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>CsV</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>Sb</mml:mi><mml:mn>5</mml:mn></mml:msub></mml:mrow></mml:math>
Dirk Wulferding, Seung‐Yeol Lee, Y. S. Choi, Qiangwei Yin, Zhijun Tu, Chunsheng Gong, Hechang Lei, Saqlain Yousuf, Jaegu Song, Hanoh Lee, Tuson Park, Kwang‐Yong Choi
Abstract
Fermi-surface fluctuations and lattice instabilities in the two-dimensional metallic kagome superconductor ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ 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 ${T}_{\mathrm{CDW}}$, with emergent $C2$ symmetry for one of the CDW amplitude modes, alluding to nematicity. In conjunction with symmetry-breaking lattice distortions, a kinklike 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.