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Date & Time: 10:30AM, May 7 (Wednesday), 2025
Host: Prof. Liang Liu
Venue: TDLI Meeting Room N601
Tencent Meeting link:
https://meeting.tencent.com/dm/ep7d3mx8vDOP Meeting ID: 689834064, no password
Abstract:
Nonlinear response properties of solids have attracted tremendous interest recently. A key motivation is that they manifest novel band geometric quantities and practical utilities that are not accessible in linear effects. A prominent example is the 2nd order intrinsic nonlinear Hall effect that can be used to detect the reversal of Neel vector in collinear antiferromagnets with combined inversion and time-reversal symmetry [1]. So far, the studies of nonlinear responses are mostly focused on the charge current, whereas the importance of nonlinear response of spin, another basic degree of freedom in solids, has not been widely appreciated. In this talk I will introduce our recent works on the 2nd order nonlinear electrical spin generation effect [2-5]. This effect lifts the stringent requirement of linear spin-orbit torque for inversion breaking and heterostructures, enabling self-generated nonlinear spin-orbit torques in centrosymmetric ferromagnets [2-4] and antiferromagnets [5]. The underlying band geometric quantities are revealed to be the Berry curvature and quantum metric in mixed momentum-magnetization parameter space. Such direct electrical manipulation of centrosymmetric magnets largely extends the material platform of magnetic memory devices. These novel effects pave the way for the emerging field of nonlinear spin-orbitronics.
References:
[1] H. Liu, J. Zhao*, Y.-X. Huang, W. Wu, X.-L. Sheng, C. Xiao*, and S. A. Yang, Intrinsic Second-Order Anomalous Hall Effect and Its Application in Compensated Antiferromagnets, Phys. Rev. Lett. 127, 277202 (2021).
[2] C. Xiao, H. Liu*, W. Wu*, H. Wang, Q. Niu, and S. A. Yang, Intrinsic Nonlinear Electric Spin Generation in Centrosymmetric Magnets, Phys. Rev. Lett. 129, 086602 (2022).
[3] C. Xiao*, W. Wu, H. Wang, Y.-X. Huang, X. Feng, H. Liu*, G.-Y. Guo*, Q. Niu, and S. A. Yang, Time-Reversal-Even Nonlinear Current Induced Spin Polarization, Phys. Rev. Lett. 130, 166302 (2023).
[4] X. Feng, W. Wu, H. Wang, W. Gao, L. K. Ang, Y. X. Zhao, C. Xiao*, and S. A. Yang*, Quantum metric nonlinear spin-orbit torque enhanced by topological bands, arXiv:2402.00532 (To appear on Materials Today Quantum).
[5] J. Cao, W. Wu, H. Liu*, S. Lai, C. Xiao*, X. C. Xie, and S. A. Yang, Nonlinear Neel Spin-Orbit Torque in Centrosymmetric Antiferromagnets, to appear on arXiv.
Biography:
Cong Xiao obtained his PhD in theoretical physics from Peking University in 2016. After that, he worked as a postdoc in the University of Texas at Austin with Prof. Qian Niu, as a Research Assistant Professor in the University of Hong Kong with Prof. Wang Yao, and as an Assistant Professor in the University of Macau. He joined Interdisciplinary Center for Theoretical Physics and Information Sciences at Fudan University on January 2025. His research interest is in transport and response properties in condensed matter physics, especially those related to Berry phase. His recent works focus mainly on novel nonlinear transport and nonlinear spintronics effects. In particular, he proposed the detection scheme of Neel vector switching by intrinsic nonlinear Hall effect, the intrinsic nonlinear planar Hall effect, the orbital and layer origin of intrinsic planar Hall effect, the scaling law of time-reversal odd nonlinear Hall effect, the nonlinear spin-orbit torque, the intrinsic nonlinear spin Hall effect, and many other novel response effects. He has published more than 50 peer-reviewed papers, including 40+ first author or corresponding author paper in high-profile journals such as Physical Review Letters and Nature Communications. Recent interests include the transport and spintronic properties in antiferromagnetic and altermagnetic materials.