Soft mode origin of charge ordering in superconducting kagome CsV3Sb5
- Philippa Helen McGuinness
- Fabian Henssler
- Manex Alkorta
- Mark Joachim Graf von Westarp
- Artem Korshunov
- Alexei Bosak
- Daisuke Ishikawa
- Alfred Q. R. Baron
- Michael Merz
- Amir-Abbas Haghighirad
- Maia G. Vergniory
- Sofia-Michaela Souliou
- Rolf Heid
- Ion Errea
- Matthieu Le Tacon
2026-05-30
Charge-density-wave (CDW) order and superconductivity coexist in the kagome metals AV 3 Sb 5 (A=K, Cs, Rb), raising fundamental questions about the mechanisms driving their intertwined phases. Here we combine high-resolution inelastic X-ray scattering with first-principles calculations to uncover the origin of CDW formation in CsV 3 Sb 5 . Guided by structure factor analysis, we identify a soft phonon mode along the reciprocal M - L direction, with the strongest effect at the L point, where the elastic scattering intensity also grows most rapidly upon cooling. First-principles calculations incorporating lattice anharmonicity and electron-phonon coupling reproduce these observations and establish a soft-mode instability at the L point as the driving mechanism of CDW formation. Despite the weakly first-order character of the transition, our results unambiguously demonstrate that the CDW in CsV 3 Sb 5 originates from a softened phonon, clarifying its microscopic origin and highlighting the central role of lattice dynamics in kagome metals.