Soft Phonon Charge-Density-Wave Formation in the Kagome Metal KV3Sb5

Abstract

A range of unusual emergent behaviors have been reported in the charge-density-wave (CDW) state of the AV3Sb5 (A=K, Rb, Cs) kagome metals, including a CDW formation process without soft phonons, which points to an unconventional CDW mechanism. Here, we use inelastic x-ray scattering to show that the CDW in KV3Sb5 forms via phonons that soften to zero energy at the CDW ordering vector (L point) around TCDW=78 K. The intensity of soft phonons exhibits a remarkable in-plane anisotropy, extending over a much larger momentum range along L−A relative to L−H, which leads to diffuse scattering common among AV3Sb5. Using first-principles calculations, we find that the momentum-dependent electron-phonon coupling (EPC) peaks at L and exhibits the same in-plane anisotropy as the phonon softening. Conversely, the electronic susceptibility does not peak at L and shows the opposite in-plane anisotropy. Our findings favor momentum-dependent EPC as the driving mechanism of the CDW in KV3Sb5, with a CDW formation process similar to that of transition metal dichalcogenides.

Source-reported materials — not catalogue approval

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