The symmetries of crystals play an important role in the properties of their phonons. When the mirror symmetries are broken, the lattice ions can display circular motion with finite angular momentum. These modes, known as chiral phonons, have recently been demonstrated in both rotating and propagating lattice motions. Usually, phonons are insensitive to magnetic fields. On the contrary, chiral phonons carry magnetic moment and directly couple to magnetic fields.
    In this talk, I will present a review of the recent progress on the study of chiral phonons using terahertz time-domain spectroscopy. Our contributions to this exciting new field will be highlighted [1-3]. In particular, I will show that the phonon magnetic moment is largely enhanced in topological materials. Furthermore, unpublished results will be discussed to provide future perspectives.
    Our research was supported by FAPESP Grants No. 2015/16191-5 and 2018/06142-5, 2021/12470-8, 2023/04245-0, and CNPq Grants No. 307737/2020-9 and 409245/2022-4.

[1] A. Baydin et al., Physical Review Letters 128, 075901 (2022).
[2] F. G. G. Hernandez et al., Science Advances 9, eadj4074 (2023).
[3] N. M. Kawahala et al., Coatings 13, 1855 (2023).