第10回物理工学科教室談話会[Prof. Tiantian Zhang・12/9(火)14:00～]

講　師：Prof. Tiantian Zhang
所　属：Associate Professor, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, China
題　目：Circularly polarized phonons and their general ab initio framework in magnetic materials
日　時：2025 年 12 月 9 日(火)14:00～
Date and Time： December 9th, 2025 (Tuesday) 14:00-
場　所：工 6 号館 3 階セミナー室 A
Place：Seminar Room A, 3rd floor, Engineering Bldg. 6

Abstract：
The terminology of chirality in phonon systems carries multiple connotations, including topological chirality and rotational chirality. The former is closely related to the pseudo-angular momentum (PAM) and can be experimentally probed using circularly polarized light, while the latter is associated with a nonzero angular momentum (AM).
At the beginning of my talk, I will introduce both types of chirality in detail and present several experimental observations, such as FeSi (the first topological phonon material), circularly polarized phonons in systems with nonsymmorphic symmetries (e.g., α-HgS and Te), and spin–phonon–induced circularly polarized phonons in Co₃Sn₂S₂. In the second part, I will introduce our recent work on developing a general ab initio framework based on molecular Berry curvature (MBC), which captures electronic-order–driven symmetry breaking in lattice dynamics and is applicable to both insulating and metallic magnets. Using Co₃Sn₂S₂ as a model system, our analysis reveals distinct microscopic origins for the E₉ and Eᵤ phonon modes.

紹介教員：村上 修一 教授（物理工学専攻）、渡辺 悠樹 准教授（物理工学専攻）