Abstract | The wavefunction of phonons encodes rich quantum information, including topological and chiral properties. In phonon systems, “chirality” carries distinct meanings: topological chirality defined by Berry curvature in k-space and rotational chirality associated with nonzero angular momentum.In this talk, I will first introduce both types of chirality and highlight key experimental observations, such as in FeSi [1] (the first material identified with topological phonons), α-HgS and Te [2], and molecular Berry curvature [3]–induced time-reversal symmetry breaking and phonon splitting in Co₃Sn₂S₂ [4].I will then present our recent work: a general ab initio framework, which captures electronic order-driven symmetry breaking in lattice dynamics and applies to both insulating and metallic magnets. Applying this framework to Co₃Sn₂S₂ reveals distinct microscopic origins for the Eg and Eᵤ phonon modes [5]. Finally, I will discuss how to directly probe the quantum geometric tensor for phonons, including its imaginary part Berry curvature and real part quantum metric components, an approach extendable to other bosonic collective excitations [6]. References: [1] T. Zhang, et al., Phys. Rev. Lett., 120, 016401 (2018) [2] Ishito, et al., Nat. Phys., 19, 35-39 (2023); T. Zhang, et al., Nano Lett., 23, 7561–7567 (2023) [3] Mead and Truhlar, J. Chem. Phys.70, 2284–2296 (1979); M.V. Berry. Proc. R. Soc. Lond. A, 392, 45-57 (1984); Saparov, et al., Phys. Rev. B, 105, 064303 (2022) [4] Yang, et al, Phys. Rev. Lett., 134, 196905 (2025); Che, et al., Phys. Rev. Lett., 134, 196906 (2025) [5] Zhang, Wang, Zhang and T. Zhang*, Sci. Adv., 12, eaed7081 (2026) [6] Wu, Oka, Murakami and T. Zhang*. arXiv: 2601.13963 (2026)
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