8月20日 美国Rutgers University吴伟达(Weida Wu)教授学术报告:Fluctuation driven topological Hall effect in two-dimensional ferromagnets


时间:8月20日上午十点
地点:唐楼A313
题目:Fluctuation driven topological Hall effect in two-dimensional ferromagnets
Weida Wu (Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA)
Abstract:Berry phase is quantum version geometric phase of wavefunction. It underscores many interesting topological phenomena especially in various extraordinary Hall effects. Among them, topological Hall effect (THE) is a real space Berry phase phenomenon originated from scalar spin chirality which is proportional to the solid angle subtended by non-coplaner spin texture (1–3). Recently THE has also been observed in static spin texture with integer Berry phase (skyrmions) in chiral magnets (4–6). While thermally driven spin chirality fluctuation has been predicted to exist in 2 dimensional chiral magnets, the resultant THE have not been observed (7). Herein, we report a surprising observation of substantial THE due to spin chirality fluctuation around the ferromagnetic transition Tc of SrRuO3 ultra-thin films, a uniaxial ferromagnet with very weak chiral interaction. The temperature, magnetic field, and thickness dependences of THE are in excellent agreement with our Monte-Carlo simulations, which provides compelling evidence of the emergence of chiral fluctuation driven topological responses.
References:
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5. Huang, S. X. & Chien, C. L. Extended Skyrmion Phase in Epitaxial FeGe(111) Thin Films. Phys. Rev. Lett. 108, (2012).
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7. Hou, W. T., Yu, J. X., Daly, M. & Zang, J. Thermally driven topology in chiral magnets. Phys. Rev. B 96, 140403(R) (2017).
Brief bio:
Dr. Weida Wu is an associate professor at the Department of Physics and Astronomy at Rutgers University. He received his BS degree from University of Science and Technology of China in 1998, MS from Northwestern University in 1999, and Ph.D. in Physics from Princeton University in 2004. He did post-doc at University of Texas at Austin in 2004-2006. Dr. Wu joined Rutgers University first as research assistant professor in 2006-2007, the as assistant professor in 2007-2012. He was promoted to associate professor with tenure in 2013. Dr. Wu’s research covers a broad range of correlated phenomena, including multiferroics and magnetoelectrics, topological quantum materials, CMR manganites, etc. For his accomplishments, Dr. Wu received CAREER Award from US NSF in 2009 and Early Career Award from US DOE in 2011. His research program is currently funded by both NSF and DOE.

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