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    Truth Forum of Materials Science: Prof.Junqiao Wu from UC-Berkeley

    Editor:yaoxx Date:2017-06-10 Hits:3292

    VO2: New Physics and New Applications
     
     
    Speaker:  Prof. Junqiao Wu 
    Affliation:  Tsinghua-Berkeley Shenzhen Institute; Department of Materials Science and Engineering, University of California, Berkeley
    Time: 10:00am-11:00am, June 19th, 2017
    Location: RM701, Chao Kuang Piu Hall of Science and Technology, Yuquan Campus, Zhejiang University
    Host: Prof. Gaorong Han, Prof. Weiqiang Han
      
     
    Abstract
     
    Vanadium dioxide (VO2) has been a model quantum material system to study strongly correlation electron physics due to its metal-insulator phase transition coupled with a structural transition that occurs at 341K. In this talk, I will discuss our recent efforts in exploring exotic physics and novel applications of VO2: 1) violation of the Wiedemann-Franz where the electronic contribution to thermal conductivity is much less than what is expected from a Fermi liquid behavior; and 2) a reconfigurable meta-canvas on which arbitrary meta-photonic devices can be written, erased and re-written. Specifically, in electrically conductive solids, the Wiedemann-Franz law requires the electronic contribution to thermal conductivity to be proportional to electrical conductivity. We discover an order of magnitude breakdown of the Wiedemann-Franz law at high temperatures ranging from 240 to 341 K in metallic vanadium dioxide in the vicinity of its metal-insulator transition. Different from previously established mechanisms, the unusually low electronic thermal conductivity is a signature of the absence of quasiparticles in a strongly correlated electron fluid where heat and charge diffuse independently. For the novel application of developing a meta-canvas, we present an all-solid, rewritable meta-canvas on which nearly arbitrary photonic devices can be rapidly and repeatedly written and erased. Using the meta-canvas, we demonstrate dynamic manipulation of optical waves for light propagation, polarization and reconstruction. The meta-canvas supports physical (re)compilation of photonic operators akin to that of field-programmable gate arrays, opening up possibilities where photonic elements can be field-programmed to deliver complex, system-level functionalities.
     
     
     
    Biosketch
     
    Prof. Junqiao Wu received a BS from Fudan University and a MS from Peking University, China, both in physics. He obtained a PhD degree from the University of California, Berkeley for work on nitride semiconductors and highly mismatched semiconductor alloys. He did postdoctoral research in the Department of Chemistry at Harvard University on phase transitions in transition metal oxides. In 2006, he started his faculty appointment at UC Berkeley where he is now a full professor, as well as a faculty scientist at Lawrence Berkeley National Laboratory. He is also a Professor in the Tsinghua-Berkeley Shenzhen Institute, and a Changjiang Adjunct Professor at Peking University. His honors include the Berkeley Fellowship, the 29th Ross N. Tucker Memorial Award, the UC Regents’ Junior Faculty Fellowship, the Berkeley Presidential Chair Fellowship, the US-NSF Career Award, the US-DOE Early Career Award, the Presidential Early Career Award for Scientists and Engineers (PECASE) from the White House, the Outstanding Alumni Award from Peking University China, and the Bakar Faculty Fellowship. The Wu group explores novel properties and applications of strongly correlated electron materials with reduced dimensions, phase transitions at the nanoscale, and optoelectronic, thermal and thermoelectric properties of semiconductor alloys and interfaces. He has made ground-breaking contributions to development and understanding of narrow-bandgap nitride semiconductors, highly mismatched semiconductor alloys, phase transitions in oxide nanomaterials, defect physics of low-dimensional semiconductors, and thermal/thermoelectric physics of novel materials. He has published over 200 papers that have received over 16,000 citations. More information can be found at http://mse.berkeley.edu/~jwu 
     
         吴军桥,教授,复旦大学物理学学士学位,北京大学物理学硕士学位,美国加州伯克利大学材料科学博士学位,美国哈佛大学物理化学专业博士后。2006年至今,在美国加州伯克利大学材料科学系担任教授,兼劳伦斯伯克利国家实验室研究员;2015年受聘为教育部第十四批长江学者讲座教授,同年受聘为清华-伯克利深圳学院纳米能源材料实验室Core PI,并担任环境科学与新能源技术中心副主任。主要奖项有:伯克利奖、Ross N. Tucker奖、美国国家基金会Career奖、美国能源部Early Career奖、2013年美国总统青年科学家奖(PECASE,美国政府授予青年科学家的最高奖项)、2015年北京大学优秀校友奖、 2017年 Bakar Faculty Fellows。 研究方向:半导体与纳米材料科学技术,强关联电子材料的低维效应、纳米尺度的相变,以及半导体复合材料的热电性能和光伏性能。迄今在国际一流刊物上发表超过200篇论文,总被引用超过16000次。拥有多个太阳能和微电机等方面的专利。在国际会议上和著名科研机构做邀请报告50多次,并曾组织多场国际会议。更多信息:http://mse.berkeley.edu/~jwu/
     
     
     
    Junqiao Wu