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Ab initio studies of chiral phonons

Andrzej Ptok

Typically, a single phonon mode realizes vibration related to linear motion. However, in the presence of n-folded (n>2) rotational symmetry, the phonon wavefunction possesses additional (geometric) phase, which allows for the realization of chiral phonons by single, non-degenerate phonon branches, i.e. circular motion of the atoms around the equilibrium positions. Previous theoretical studies demonstrated that chiral phonons can be found in ideal two-dimensional hexagonal lattices [1,2]. Here, I will present our results of ab initio studies of the chiral phonons in several compounds, such as CoSn-like systems (with P6/mmm symmetry, and containing both kagome and honeycomb sublattices) [3], magnetic topological insulators TBi2Te4 (T=Mn,Fe) [4], binary compounds ABi (A=K,Rb,Cs) containing chiral Bi chains [5], and orthorhombic ternary YAlSi compound [6]. References [1] L. Zhang and Q. Niu, Phys. Rev. Lett. 115, 115502 (2015). [2] H. Chen, W. Wu, S. A. Yang, X. Li, and L. Zhang, Phys. Rev. B 100, 094303 (2019). [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. Kobiałka, M. Sternik, and A. Ptok,  Phys. Rev. B 105, 214304 (2022). [5] J. Skórka, K.J. Kapcia, P.J. Jochym, and A. Ptok, Matter. Today Commun. 35, 105888 (2023). [6] S. Basak and A. Ptok, Crystals 12 , 436 (2022).