Superfluidity in Quantum Hall Bilayers

by Prof. Herbert Fertig (Indiana University)

Tuesday 20 Jul 2010, 14:15 → 15:15 Europe/Stockholm

In this talk I will review some of the ideas and experiments suggesting that quantum Hall bilayers near filling factor 1 may form an exciton condensate state, leading to the possibility of superflow for counterflowing currents in the two layers. In real experiments, dissipationless transport appears to emerge, it at all, only at zero temperature, so that the observed superfluidity is at best imperfect. This appears likely to be due to disorder, which can flood the system with merons -- vortex-like excitations -- even at zero temperature. I will discuss a "coherence network" model which incorporates the presence of these objects in the groundstate, and qualitatively captures much of the physics observed in experiment. Finally I will discuss the results of drag experiments in this system, where interlayer coherence and quantum Hall physics conspire in such a way that one can probe different types of merons with measurements on different layers.