Phase Fluctuations in Superconductors

by Prof. Pratap Raychaudhuri (Tata Institute of Fundamental)

Tuesday 10 Jul 2012, 16:00 → 18:00 Europe/Rome

Aula Conversi (Dipartimento di Fisica - Ed. G. Marconi)

A superconductor consists of pairs of electrons, bound through weak attractive interaction (Cooper pairs), which condense in a collective phase-coherent quantum state. The superconducting state is thus described by a complex order parameter with an amplitude and a phase, that correspond to the binding energy of Cooper pairs and to the phase of the condensate, respectively. Within the conventional description of superconductivity, the occurrence of a zero-resistance state is associated with a non-zero amplitue; the phase is believed to play a negligible role, unless one goes to reduced length scales, i.e. Josephson Junctions formed through a weak link between two superconductors, superconducting films in the 2D limit or one-dimensional systems such as superconducting nanowires. However, in the past few years, a series of experiments have shown that in certain situations, phase fluctuations can play an important role and lead to a destruction of the zero-resistance state well before the gap goes to zero, even in 3D superconductors. In this talk, I will give an overview the variety of phenomena associated with phase fluctuations both in low-dimensional and bulk superconductors, and describe our experimental investigations on the role phase fluctuations in the strongly disordered conventional superconductor, NbN.