Interaction and disorder in bilayer counterflow transport at filling-factor one

We study high-mobility, interacting GaAs bilayer hole systems exhibiting counterflow superfluid transport at total filling-factor ν=1. As the density of the two layers is reduced, making the bilayer more interacting, the counterflow Hall resistivity (ρxy) decreases at a given temperature, while the counterflow longitudinal resistivity (ρxx), which is much larger than ρxy, hardly depends on density. On the other hand, a small imbalance in the layer densities can result in significant changes in ρxx at ν=1, while ρxy remains vanishingly small. Our data suggest that the finite ρxx at ν=1 is a result of mobile vortices in the superfluid created by the ubiquitous disorder in this system.