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The ideal two-dimensional kagome lattice has attracted significant attention due to its characteristic electronic band structure features. Unlike the honeycomb lattice, which exhibits Dirac and saddle points, the kagome lattice also hosts an ideal flat band. This unique lattice structure corresponds to rich physics, especially in the context of electronic properties. In several compounds containing the kagome sublattice, the realization of charge density waves (CDW) at low temperatures has been reported.
First, AV3Sb5 (A = K, Rb, Cs) compounds are rare examples where CDW coexists with superconductivity. The CDW is realized through atom displacement within the V-kagome sublattice [1]. Second, FeGe exemplifies a case where CDW is induced by correlation-driven phonon softening, resulting in a significant modification of the Ge atom [2]. In both cases, new system symmetries can be identified through phonon spectra analyses.
Lattice dynamics can also lead to intriguing findings. For CoSn-like compounds (P6/mmm symmetry), where both kagome and honeycomb lattices are present, we have discovered chiral phonons [3]. Additionally, in some cases, imaginary soft modes are observed, leading to new symmetries. In our study, we predicted the crystal structure of RhPb with P-62m symmetry (containing a distorted kagome lattice), which was confirmed experimentally [4].
In summary, studies of lattice dynamics can be a valuable tool to confirm [5] or negate [6] the realization of structures containing kagome-like sublattices.
[1] A. Ptok, A. Kobiałka, M. Sternik, J. Łazewski, P.T. Jochym, A. M. Oleś, and P. Piekarz, Phys. Rev. B 105, 235134 (2022).
[2] A. Ptok, S. Basak, A. Kobiałka, M. Sternik, J. Łazewski, P. T. Jochym, A. M. Oleś, and P. Piekarz, Phys. Rev. Materials 8, L080601 (2024).
[3] A. Ptok, A. Kobiałka, M. Sternik, J. Łazewski, P. T. Jochym, A. M. Oleś, S. Stankov, and P. Piekarz, Phys. Rev. B 104, 054305 (2021).
[4] A. Ptok, W.R. Meier, A. Kobiałka, S. Basak, M. Sternik, J. Łażewski, P.T. Jochym, M.A. McGuire, B.C. Sales, H. Miao, P. Piekarz, and A.M. Oleś, Phys. Rev. Research 5, 043231 (2023).
[5] S. Basak and A. Ptok, Materials 16, 78 (2023).
[6] A. Ptok, Physical Review B 109, 216501 (2024).
