报告题目 (Title)：Nonreciprocal Phonons in PT-Symmetric Antiferromagnets（PT对称反铁磁体中的非互易声子）
报告人 (Speaker)：牛谦 教授（中国科学技术大学）
报告时间 (Time)：2025年7月17日（周四）16:00-18:00
报告地点 (Place)：宝山校区G601
邀请人(Inviter)：钟建新
主办部门：量子科技研究院/理学院物理系
报告摘要：
Phonon nonreciprocity, indicating different transport properties along opposite directions, has been observed in experiments under a magnetic field. We show that nonreciprocal acoustic phonons can also exist without a magnetic field or net magnetization. We identify crucial contributions in phenomenological elastic theory. In PT symmetric antiferromagnets, we find two terms, dubbed flexoviscosity and flexo torque, that induce phonon nonreciprocity. The microscopic origin of these terms is attributed to the derivatives of molecular Berry curvature, manifested as emergent nonlocal magnetic fields on phonons. The symmetry breaking that originated from spin order is transferred to the phonon system through spin-orbit coupling, where the orbital degree of freedom affects the lattice dynamics directly. By electrically breaking inversion symmetry and modifying the spin-orbit coupling, we find extra contributions and show that both the phonon nonreciprocity and helicity can be controlled and enhanced. Importantly, the phonon nonreciprocity is an odd function of the Néel vector, serving as an indicator of the order parameter.
