Soft mode origin of charge ordering in superconducting kagome CsVSb

Source: PubMed Central Open Access, NCBI / U.S. National Library of Medicine

Charge-density-wave (CDW) order and superconductivity coexist in the kagome metals AVSb(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 CsVSb. Guided by structure factor analysis, we identify a soft phonon mode along the reciprocal-direction, with the strongest effect at thepoint, 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 thepoint as the driving mechanism of CDW formation. Despite the weakly first-order character of the transition, our results unambiguously demonstrate that the CDW in CsVSboriginates from a softened phonon, clarifying its microscopic origin and highlighting the central role of lattice dynamics in kagome metals. Abs1 Charge-density-wave (CDW) order and superconductivity coexist in the kagome metal CsV3Sb5. Here, via inelastic X-ray scattering in combination with first-principles calculations, the authors establish a soft-phonon-mode instability at the L point as the driving mechanism of CDW formation. Abs2 web-summary