讲座题目：Twisted magnon as a magnetic tweezer 

讲座时间：2021年6月7日 14:10分

讲座地点：成龙校区办公楼125会议室

讲座内容：Wave fields with spiral phase dislocations carrying orbital angular momentum (OAM) have been realized in many branches of physics, such as for photons, sound waves, electron beams, and neutrons. However, the OAM states of magnons (spin waves)—the building block of modern magnetism—and particularly their implications have yet to be addressed. Here, we theoretically investigate the twisted spin wave generation and propagation in magnetic nanocylinders. The OAM nature of magnons is uncovered by showing that the spin-wave eigenmode is also the eigenstate of the OAM operator in the confined geometry. Inspired by optical tweezers, we predict an exotic “magnetic tweezer” effect by showing skyrmion gyrations under twisted magnons in the exchange-coupled nanocylinder-nanodisk heterostructure, as a practical demonstration of magnonic OAM transfer to manipulate topological spin defects. Our study paves the way for the emerging magnetic manipulations by harnessing the OAM degree of freedom of magnons.

报告人简介：

      曹云姗，1985年生于贵州。2007年毕业于北京师范大学物理系，2012年毕业于北京大学物理学院，获理论物理博士学位，随后前往荷兰代尔夫特理工大学从事博士后研究工作三年。2016年初回国参加工作，现任电子科技大学电子学院副教授。主要研究方向为自旋电子学，磁光耦合，磁动力学，生物导航以及量子输运等。相关研究工作在磁性材料基础，磁性存储器，磁力探测仪，生物磁性导航等方面都有重要意义。

报告题目：A spin-wave driven skyrmion diode under transverse magnetic fields 

报 告 人：宋玲玲（博士研究生）

报告内容：A diode, a device allowing unidirectional signal transmission, lies at the heart of modern information technology as a fundamental element of logic operations. Here, we study the motion of the skyrmion driven by the spin wave (SW) in the presence of a transverse magnetic field. We show that the external magnetic field leads to a shift of SW dispersion relation and induces an asymmetric skyrmion propagation when SWs are injected from opposite sides. Based on this finding, we propose the concept of a SW-driven skyrmion diode. We numerically compute the spin-wave transport coefficients to quantify the number of reflected magnons, which explains the skyrmion velocity asymmetry. Our results offer a new insight to design skyrmion devices embracing chiral SWs.

报告题目：Observation of the higher-order topological states in electric circuit

报 告 人：杨欢欢（博士研究生）

报告内容：Higher-order topological insulator (HOTI) represents a new phase of matter, the characterization of which goes beyond the conventional bulk-boundary correspondence and is attracting significant attention by the broad community. Recently, topolectrical circuits have emerged as a simple yet very powerful platform for studying topological physics that are challenging to realize in condensed-matter systems. Here, we present an experimental observation of second-order corner states characterized by the Z3 Berry phase in topolectrical circuits. We demonstrate theoretically and experimentally that the localized second-order topological states are protected by a generalized chiral symmetry of tripartite lattices, and they are pinned to “zero energy.” By introducing extra capacitors within sublattices in the circuit, we are able to examine the robustness of the zero modes against both chiral-symmetry-conserving and breaking disturbances. Further, we report the first experimental realization of the square-root HOTI in in a hybrid honeycomb-kagome circuit. We show theoretically and experimentally that the square-root HOTI inherits the feature of wave function from its parent with corner states pinned to nonzero energies. The topological feature is fully characterized by the bulk polarization. Our results experimentally substantiate the emerging HOTI and pave the way to realizing exotic topological phases that are challenging to observe in condensed matter physics。