Condensed Matter Physics Seminar

Disordered Superfluidity in the Quantum Hall Bilayer

Professor H. Fertig
Indiana University
Tuesday, May 3, 2005
Higgins 235, 2pm

Superfluids and superconductors are known to possess a unique stiffness related to the phase of their groundstate wavefunctions. Under appropriate circumstances, double layer quantum Hall systems possess an analogous stiffness that may be understood in terms of a condensation of particle-hole pairs. The relation between these systems has motivated both theoretical and experimental efforts to find properties in the bilayer quantum Hall system usually associated with superfluids. Most prominently, effects reminiscent of Josephson tunneling and counterflow superfluidity have been observed, although there is considerable dissipation whose origin is not understood. We study this system using both a renormalization group analysis and Langevin dynamics simulations. We find that vortices have a very unusual thermal deconfinement transition in this system, and can also be broken apart at low temperature by disorder. A model that incorporates the disorder leads to a coherence network in which puddles of high vortex density, with the superfluid stiffness effectively eliminated, are separated by narrow regions of coherence. We show that this model produces dissipation in linear response that qualitatively agrees with experiment for both tunneling and counterflow geometries.