Superconductor-Insulator Transitions in Two-Dimensions

Aharon Kapitulnik
Department of Physics, Stanford University

In this talk we will discuss the behavior of thin superconducting films at very low temperature as a function of disorder and applied magnetic field. Transport measurements in a perpendicular magnetic field show distinct regimes of strongly fluctuating order-parameter amplitude and phase, and reveal a wide range of insulator strength in samples with differing disorder, despite the similarity in behavior near the superconductor-insulator transition. An intervening metallic phase is also found in films with weak disorder. A detailed study of the superconductor-insulator transition in many films suggests that results for a variety of materials with different strength of disorder can be collapsed onto a single phase diagram. The data display two clear branches, one with weak disorder and an intervening metallic phase, the other with strong disorder.