报告题目：Statistics of thermomagnetic breakdown in Nb superconducting films
 报告人：Professor Alejandro V. Silhanek
             Département de Physique, Université de Liège, Belgium

报告时间：2019年4月11日（星期四）上午10:00-11:00
报告地点：M楼236会议室
   联系人：朱北沂 8264-9927

报告摘要：
As dissimilar as they might appear, lightning during a dielectric breakdown, failure ofinterconnects in integrated circuits, snow avalanches on mountain slopes, or popcornexplosion share a common physics ground corresponding to the triggering of acatastrophic event when a threshold stress is exceeded. Interestingly, even if the sameexperience is repeated under identical environmental conditions, the event will nothappen at exactly the same threshold stress. The question as to whether the statisticaldistribution of this threshold stress follows a universal law for all phenomena isexperimentally difficult to answer, since exceeding the threshold point brings alongdramatic consequences leading to irreversible changes in the system. Remarkably,superconducting materials offer a unique opportunity to investigate the statisticaldistribution of similar catastrophic events consisting of non-destructive magnetic fluxavalanches in the same sample and thus ruling out the spreading factors associated tounavoidable uncontrollable variations in the replicas of the system.

Using the magneto-optical imaging technique to record images of the magnetic field ina superconducting Nb sample, we cycled 2000 times the same thermomagneticbreakdown experiment under identical conditions. Based on this experience, wedetermined the probability density function of the threshold field of thermomagneticbreakdown and tracked its temperature dependence with unprecedented resolution.Strikingly, we identified a bimodal distribution of the threshold field, with a transitionfrom filamentary to dendritic branching avalanches, representing a unique fingerprintassociated to avalanches initiated by a thermomagnetic instability, with no counterpartin other catastrophic events such as earthquakes or granular avalanches.

报告人简介：
Alejandro Silhanek obtained his Ph.D. degree at Instituto Balseiro (Argentina) in 2002 under the supervision of Prof. L Civale. His thesis was devoted to the experimental study of high temperature superconductors with defects introduced by heavy-ion irradiation. Afterwards he acquired experience on nanofabrication at the KULeuven in Belgium working in the group of Prof. V. Moshchalkov followed by a postodoctal stay at the High Field National Laboratory, Los Alamos (USA) working on micro-calorimetric techniques. Since 2011, he is Professor of the Physics Departement of the University of Liège and head of the research group “Experimental Physics of Nanostructured materials.” He has co-authored over 150 publications in diverse topics including nanostructured superconducting, metallic, semiconductors, and magnetic systems, planar plasmonic metamaterials, biomicrofluidics devices, heavy-fermions, and quantum-critical points.