  We study interacting GaAs bilayer hole systems, with very small interlayer
tunneling, in a counterflow geometry where equal currents are passed in
opposite directions in the two, independently contacted layers. At low
temperatures, both the longitudinal and Hall counterflow resistances tend to
vanish in the quantum Hall state at total bilayer filling $\nu=1$,
demonstrating the pairing of oppositely charged carriers in opposite layers.
The temperature dependence of the counterflow Hall resistance is anomalous
compared to the other transport coefficients: even at relatively high
temperatures ($\sim$600mK), it develops a very deep minimum, with a value that
is about an order of magnitude smaller than the longitudinal counterflow
resistivity.
