7月24日 美国科罗拉多州立大学Prof. Mingzhong Wu学术报告:Nontrivial Nature and Penetration Depth of Topological Surface States in SmB6 Thin Films


题目:Nontrivial Nature and Penetration Depth of Topological Surface States in SmB6 Thin Films
报告人:Prof. Mingzhong Wu, Department of Physics, Colorado State University, Fort Collins, CO 80523, USA
时间:2018年7月24日(星期二)上午 9:30
地点:唐仲英楼A213

Abstract:Being the first rare earth mixed valence system and the first Kondo insulator, SmB6 may very likely be the first topological Kondo insulator too. Recent studies have confirmed the existence of topological surface states (TSS) and surface chiral spin textures in single-crystal SmB6 bulk materials, but the nontrivial nature and depth scale of the TSS remain unresolved. In this talk I will report our recent work on the use of spin pumping to study the nontrivial feature of the TSS in SmB6.1 Our experiments used SmB6 thin films grown on magnetic insulator Y3Fe5O12 (YIG) bulk materials. Upon the excitation of magnetization precession in the YIG, a pure spin current is generated that flows from the YIG into the SmB6 film and produces, via spin-orbit coupling, a lateral electrical voltage in the SmB6 film. The spin-pumping voltage signal becomes considerably stronger as the temperature decreases from 150 K to 10 K. Such an enhancement most likely originates from the spin-momentum locking feature of the TSS of the SmB6 film and may thereby serve as a strong evidence for the nontrivial nature of the TSS. The voltage data also show a unique film thickness dependence that suggests a TSS depth of about 32 nm for the TSS. The data also indicate a spin diffusion length of about 39 nm in the SmB6 film. The spin-pumping results are supported by temperature-dependent transport measurements and theoretical analyses using a tight binding model.

1 “Nontrivial nature and penetration depth of topological surface states in SmB6 thin films” Tao Liu, Yufan Li, Lei Gu, Junjia Ding, Houchen Chang, P. A. Praveen Janantha, Boris Kalinikos, Valentyn Novosad, Axel Hoffmann, Ruqian Wu, C. L. Chien, and Mingzhong Wu, Physical Review Letters 120, 207206 (2018).

Biography: Mingzhong Wu received his Ph.D. in Solid State Electronics from Huazhong University of Science and Technology in 1999, joined the faculty of Colorado State University (CSU) in 2007, and is currently a Professor of Physics and the Director of PRSE-Designated Center for Advanced Magnetics at CSU. He is interested in many research topics in magnetics. His current research areas include magnetization dynamics, spintronics, nonlinear spin waves, thin film growth, and microwave magnetic materials and devices. He has authored about 135 publications, including 19 articles in Physical Review Letters, 2 in Nature Physics, and 3 in Nature Communications. He has also co-edited a book on magnetic insulators. Mingzhong Wu was an Editor for IEEE Magnetics Letters (2012-2016). Currently, he is serving as an Editor for Physics Letters A and is also on the Editorial Advisory Board of Journal of Applied Physics and the Editorial Board of Journal of Magnetism and Magnetic Materials. He served as the Education Committee Chair of the IEEE Magnetics Society in 2012-2015 and is currently the Financial Chair of the society. He was the Program Co-Chair for the 2017 Annual Magnetism and Magnetic Materials Conference.

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