报告题目：Quasi-periodic magnetic flux avalanches in doubly-connected superconductors
报告人：Professor Yosef Yeshurun
           Institute of Superconductivity and Institute of Nano Technology, Department of Physics, Bar-Ilan University, Ramat-Gan, Israel

报告时间：2019年11月11日（星期一）上午10:00-11:00
报告地点：M253会议室
   联系人：朱北沂  8264-9927

报告摘要：
     Magneto-optical imaging (MOI) has been established as a powerful tool for studying magnetic flux distributions in superconductors. In particular, this technique has been extensively utilized in the study of flux penetration in form of dendritic avalanches in a variety of superconducting films. it was found that with increasing field above a certain threshold, , dendrites penetrate the samples at random fields and propagate along paths that terminate inside the sample. In this talk I will focus on our recent findings, revealing a dramatic effect of the sample topology on the dendritic phenomenon. Specifically, MOI of Nb rings, open rings and strips, reveal that that dendrites in a ring can cross the entire width of the sample. Such dendrites appear when the difference between the applied field and the average field inside the central hole reaches a certain threshold level, . With increasing applied field, this condition is reached quasi-periodically as a crossing dendrite creates momentarily a hot channel through which flux flows into the central hole, balancing the field inside the hole with that outside the ring. The threshold  differs in magnitude from the onset field  of magnetic instability, and exhibits qualitatively different dependence on the rim width.

报告人简介：
Prof. Yosef Yeshurun, Director of the Superconductivity Institute and Head of the Center for Magnetic Measurements, completed his university education in Israel, continued with advanced post-doctoral research at the University of Illinois, Urbana-Champaign, and returned to Bar-Ilan University as a tenured member at the Department of Physics. In this Department he set up a unique laboratory for magnetic measurements, undertaking a range of experimental solid-state research studies in a number of fields, such as one-dimensional organic conductors, spin glasses, amorphous metals and superconductors. He has had close scientific ties with universities and research institutes in Israel and throughout the U.S.A., France, Germany, Denmark, China and Japan. He spent sabbatical years at IBM research laboratories at Yorktown Heights, Imperial College, London, New York University (NYU) and City College of New York (CCNY). He also was a visiting professor for shorter period of times at research institutes in Denmark, France, UK, China and USA, where he was also appointed Fellow of the American Physical Society. His research activities in Israel and abroad are sponsored by national and international research foundations. Prof. Yeshurun has served in many capacities at Bar-Ilan University, including Head of the Department of Physics, Dean of Students, Vice-Rector and Rector of the University. He also served as an active member of Israeli national bodies such as the Council for Higher Education, the National Research and Development Council, and the National Steering Committee for Superconductivity.