Lecturer: Prof. Aviad Frydman Affiliation: Department of Physics, Bar-Ilan University Abstract: The superconductor-insulator transition (SIT) is regarded as a prototype of a quantum phase transition. Varying a non- thermal tuning parameter, such as disorder, causes the system to switch from a perfect conductor to a perfect insulator. Despite the long history of research in the field, the nature of the SIT and especially that of the insulating phase is still very much under debate and the full understanding awaits new and innovation methods. A quantum phase transition is governed by quantum rather than thermal fluctuations. For the SIT these are manifested by collective order-parameter amplitude and phase modes (known as Higgs and Goldstone modes) that are predicted to become prominent in the vicinity of the quantum phase transition. In my talk I will describe two new experiments on systems close to the SIT. The first is a study of the ac conductivity in thin disordered superconducting films close to the SIT using terahertz spectroscopy. The second is a measurement of specific heat of thin granular superconductors through the SIT. Both experiments show excess electronic spectra or degrees of freedom which are identified as collective modes close to the quantum phase transition. ‏האירוע הזה כולל שיחת וידאו ב-Google Hangouts. הצטרף: https://hangouts.google.com/hangouts/_/mail.huji.ac.il/condensed?hceid=b...