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Experimental probing of quantum criticality at the Superconductor-Insulator Quantum Phase Transition

Date: 2017-11-16
Time: 10:00
Venue: M253会议室
Speaker: Professor Aviad Frydman

Department of Physics, Bar Ilan University, Israel

The superconductor-insulator transition (SIT) is a prototype of a quantum phase transition which is very versatile experimentally: varying a non-thermal tuning parameter such as disorder, thickness, composition, magnetic field or gate-voltage causes the system to switch from a superconductor to an insulator at zero temperature.
Unlike their classic counterparts, quantum phase transitions are governed by quantum fluctuations rather than thermal fluctuations. The direct experimental study of such fluctuations close to the SIT is rather challenging. So far research has mainly concentrated on dc resistivity based measurements such as transport and magnetoresistance and on global and local tunneling spectroscopy. These cannot provide explicit information on the critical behavior through the transition.
In my talk I will describe two experimental efforts designed to measure signatures of quantum fluctuations close to quantum criticality. The first experiment utilizes a unique, highly sensitive, setup to measure the specific heat of ultrathin Pb films through the gtowards the SIT thus signaling quantum criticality. The second experiment is a scanning squid measurement able to probe local susceptibility in TiNbN films close to the quantum transition. These studies reveal electronic superconducting granularity which fluctuates in time and space at temperatures well below Tc. The temperature regime of these fluctuations grows as the SIT is approached indicating their quantum nature.
I will discuss the significance of these results and their contribution to understanding the electronic processes in the vicinity of the quantum phase transition.

AviadFrydman is a professor of physics and the head of the nano-electronic laboratory in Bar Ilan University, Israel. He completed his Ph.D. degree in the Hebrew University of Jerusalem and was a postdoctoral researcher in University of California, San Diego Since 1999 he has been a faculty member of Bar Ilanuniversity and spent two visiting-professor years in Yale University and Neel Institute of Grenoble. His research interests include experimental study of the electronic properties of low dimensional systems, nano dots, 1D wires, ultrathin films and granular arrays, focusing on ferromagnets and superconductors.

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