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 nu=1. As the density of the two layers is reduced, making the bilayer more interacting, the counterflow Hall resistivity (rho(xy)) decreases at a given temperature, while the counterflow longitudinal resistivity (rho(xx)), which is much larger than rho(xy), hardly depends on density. On the other hand, a small imbalance in the layer densities can result in significant changes in rho(xx) at nu=1, while rho(xy) remains vanishingly small. Our data suggest that the finite rho(xx) at nu=1 is a result of mobile vortices in the superfluid created by the ubiquitous disorder in this system.