Abstract:

Superconductivity is a manifestation of the formation of a collective, many-body state of electron pairs. Application of a magnetic field (B) weakens superconductivity and in 2D films, the system is forced into an insulating state above a critical field. I will show results from our experiments on disordered, thin films of amorphous indium oxide that suggest that a new collective state emerges in the the B-induced insulating state. An experimental phase diagram is drawn that includes the superconducting state, a transition to a "Bose" insulator and an eventual crossover to a "Fermi" insulator.