Phonon anharmonicity effects in the charge density wave orders of vanadium-based kagome metals

Kagome materials boast an abundance of rich phenomena, including quantum-spin-liquid states, fractionalized topological phases, anomalous Hall effect, charge density waves, and superconductivity, to name a few. Recently, a family of kagome materials AV₃Sb₅ (A= K, Cs, Rb) has attracted considerable attention. In particular, CsV₃Sb5 (a Z₂ topological metal) is experimentally shown to have a superconducting ground state and host multiple competing electronic orders, most notably, charge-density waves (CDW) around 90K, and exhibits interesting transport properties, such as field-tuned chiral transport. Additionally, a related class, RV₆Sn₆ (Y, Sc, Gd, Ho), specifically ScV₆Sn₆ has been shown to host unconventional CDWs, endowing it with multiple lattice instabilities and anomalous electrical transport, where the resistivity decreases through TCDW. We explore the implications of electron-phonon interactions in CDW formation and study their effect on the electrical and thermal properties of this system. We will also discuss how, for example, phonon anharmonicity stabilizes the soft Sn vibrational flat modes at elevated temperatures whose collapse gives rise to a CDW phase transition.