Switching of chiral phonons in ferroelectrics

Chirality is one of the major topics in recent condensed matter physics due to chirality-induced functionalities and topological textures relating to symmetry breaking, e.g., in van der Waals materials. Driving a chiral mode can be a unique approach to manipulating ultrafast emergent phenomena and corresponding dynamics. Recently, our group successfully observed chiral phonons in chiral crystals of α-quartz using circularly polarized RIXS [Nature 618, 946 (2023)]. In principle, chiral phonons exist in other non-centrosymmetric crystals, such as polar (ferroelectric) materials, which we recently observed for a non-chiral but polar crystal LiNbO3. This result suggests that we can manipulate phonon chirality by flipping the polarization. We plan to demonstrate in situ electric field switching on free-standing (FS) films of BaTiO3 (BTO) using circularly polarized RIXS at the oxygen K-edge. Our results will open the possibility of manipulating phonon chirality and associated phonon angular

手性（Chirality）是当前凝聚态物理的核心研究主题之一，这源于手性诱导的功能特性以及与对称性破缺相关的拓扑纹理——例如范德瓦尔斯（van der Waals）材料中存在的此类结构。激发手性模式，可作为调控超快涌现现象及其对应动力学过程的独特手段。近期，我们团队利用圆偏振共振非弹性X射线散射（circularly polarized Resonant Inelastic X-ray Scattering，简称RIXS）在α-石英（α-quartz）的手性晶体中成功观测到了手性声子[Nature 618, 946 (2023)]。理论上，手性声子也存在于其他非中心对称晶体中，比如极性（铁电）材料：我们近期便在非手性但具有极性的铌酸锂（LiNbO3）晶体中观测到了此类声子。该结果表明，我们可通过翻转极化方向来调控声子的手性。我们计划在氧K边（oxygen K-edge）能区，利用圆偏振RIXS对钛酸钡（BaTiO3，简称BTO）的自支撑（free-standing，简称FS）薄膜开展原位电场切换实验。本研究成果将为调控声子手性及其相关的声子角开辟全新的可能性。