Soft Phonon Charge-Density-Wave Formation in the Kagome Metal KV_{3}Sb_{5}

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Unusual emergent behaviors observed in AV3Sb5 kagome metals' charge-density-wave (CDW) state.
• Previous studies suggested unconventional CDW mechanisms due to a lack of soft phonons.

Purpose of the Study:

• Investigate the mechanism of CDW formation in KV3Sb5.
• Clarify the role of phonons and electron-phonon coupling (EPC) in CDW emergence.

Main Methods:

• Inelastic X-ray scattering (IXS) to probe phonon behavior.
• First-principles calculations to determine electron-phonon coupling and electronic susceptibility.

Main Results:

• Observed phonon softening to zero energy at the L point around 78 K, confirming a conventional CDW mechanism.
• Identified in-plane anisotropy in soft phonon intensity and momentum-dependent EPC, both peaking at the L point.
• Electronic susceptibility showed opposite anisotropy and did not peak at L.

Conclusions:

• Momentum-dependent electron-phonon coupling is the primary driver of the CDW in KV3Sb5.
• The CDW formation process in KV3Sb5 resembles that of transition metal dichalcogenides.
• The observed phonon anisotropy explains diffuse scattering phenomena in AV3Sb5 materials.