报告题目：Discovery of universal phonon thermal Hall effect in crystals

报告人：李世燕  复旦大学

报告时间：2024年8月16日 星期五 16:00

报告地点：M253

邀请人：应天平

联系人：郭建刚

联系电话：82649905

报告摘要：

Thermal Hall effect (THE) in insulator is a remarkable phenomenon that arises from the motion of chargeless quasi-particles under a magnetic field. While magnons or exotic spin excitations were considered as the origin of THE in some magnetic materials, there are more and more evidences suggesting that phonons play a significant role. However, the mechanism behind phonon THE is still unknown. In this talk, we report the observation of THE, including planar THE, in a broad range of non-magnetic insulators and semiconductors: SrTiO₃, SiO₂ (quartz), MgO, MgAl₂O₄, Si and Ge. While the presence of antiferrodistortive domains in SrTiO₃ and chiral phonons in SiO₂ may complicate the interpretation of THE, the striking observations of THE in trivial insulators MgO and MgAl₂O₄, as well as in high-purity intrinsic semiconductors Si and Ge, demonstrate that phonon THE is a universal property of crystals. Without other effects on phonons such as from magnons, this universal phonon THE is characterized by a scaling law of |κ_xy| ~ κ_xx². Our results experimentally discover a fundamental physics of phonons in magnetic field, which should come from the direct coupling between atom vibrations and the field. Starting from this universal phonon THE in crystals, all previous interpretations of THE in magnetic or non-magnetic materials need to be reconsidered [1].

I will also briefly discuss another topic: Layer-dependent superconductivity in iron-based superconductors CsCa₂Fe₄As₄F₂ and CaKFe₄As₄ [2].

[1] Xiaobo Jin et al., arXiv:2404.02863.

[2] Ke Meng et al., Nano Letters 24, 6821 (2024).

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