Anharmonic treatment of the charge-density wave in the kagome-metal CsV3Sb5.

After three years since the discovery of the AV3Sb5 (A=Cs,Rb,K) kagome-metals [1], the structure and origin of the charge-density wave (CDW) state still remain elusive. Since the high-symmetry structures stabilized around 90 K are unstable in the harmonic approximation, strong anharmonicity has to be a major ingredient in these systems and advocates for a more detailed analysis.

Here, we make a non-perturbative treatment of anharmonicity [1] in order to solve the CDW by first-principles calculations. Due to anharmonic corrections, the M=(0.5,0,0) phonon is stabilized, thus, contradicting the usual nesting-driven-CDW picture in kagome-systems. On the other hand, the L=(0.5,0,0.5) phonon remains unstable and is responsible for the purely 3-dimensional CDW. These results restrict the possible order parameters and do not account for the collective condensation of M and L modes considered in the literature.

[1] Ortiz, B. R., Gomes, L. C., Morey, J. R., Winiarski, M., Bordelon, M., Mangum, J. S., Oswald, I. W. H., Rodriguez-Rivera, J. A., Neilson, J. R., Wilson, S. D., Ertekin, E., McQueen, T. M., & Toberer, E. S. (2019, September 16). New kagome prototype materials: discovery of KV3Sb5,RbV3Sb5 , and CsV3Sb5. Physical Review Materials, 3(9).

[2] Monacelli, L., Bianco, R., Cherubini, M., Calandra, M., Errea, I., & Mauri, F. (2021, July 13). The stochastic self-consistent harmonic approximation: calculating vibrational properties of materials with full quantum and anharmonic effects. Journal of Physics: Condensed Matter, 33(36), 363001.