Topology and chirality of fermionic quasiparticles have enabled exciting discoveries, including quantum anomalous Hall liquids and topological superconductivity. Recently, topological and chiral phonons emerge as new and fast-evolving research directions. While these concepts are separately developed, they are intimately connected in the context of Weyl phonons. The couplings between chiral and topological phonons with various electronic and magnetic quasiparticles are predicted to give rise to new quantum states and giant magnetism with fundamental and applicational interests, ranging from quantum information science to dark matter detectors.

Unlike electrons, phonons are charge neutral, spin zero and orbital free, which makes the means of modulating phonons very limited. Thus, introducing both topological and chiral degrees of freedom is helpful and vital to understand phonon-involved physical processes and applications. Topological phonons are novel collective lattice excitations that carry non-trivial topological invariants and pseudo-spin tectures, as shown in Fig. 1. Chiral phonons refer to phonon modes that have finite angular momentum (AM) and widely present in non-centrosymmetric materials. In this comment, we overview theoretical understandings of topological and chiral phonons and elucidate the fundamental connection between topology and chirality in the context of Weyl phonons. We discuss recent experimental progresses related to topological and chiral phonons and open questions and future research directions.

Figure 1: Chiral and topological phonons in quantum materials. Topological phonons are characterized by non-trivial topological invariants, associated with nontrivial pseudospin texture around the band degeneracies and topological surface states. Chiral phonons are described by phonon modes with finite AM, associated with circular atomic motions in the real space, thus also referred to as circularly polarized phonons. These two concepts are fundamentally connected in 3D non-centrosymmetric materials. Left panels show the spiral surface state, the pseudo-spin texture, and band dispersion of the twofold quadruple Weyl phonon with C=+4. Right panels show that in the vicinity of twofold quadruple Weyl point, the corresponding lattice motion is chiral with finite AM. The general relation between Weyl and chiral phonons are highlighted in the middle panel. In non-centrosymmetric materials, Weyl phonons are special type of chiral phonons. Chiral phonons are, however, not necessarily topological.

Tiantian Zhang, Shuichi Murakami & Hu Miao, Weyl phonons: the connection of topology and chirality, Nature Communications (2025). 

DOI: https://doi.org/10.1038/s41467-025-58913-0