Glassy behavior in quantum Hall bilayers

Interlayer tunneling in quantum Hall bilayer systems is investigated via numerical simulations of the classical two dimensional XY model with a symmetry-breaking field. It is shown that sufficiently strong disorder induces strings of overturned spins and unpaired vortices to proliferate through the system. This string glass state supports low energy excitations which lead to anomalously large dissipation when a small tunneling is present, as observed in experiment. Strong interlayer tunneling currents can depin the strings and lead to nearly normal dissipation above a critical current. This depinning phenomenon also explains the behavior of experiments in parallel magnetic fields.