We show that in a nonequilibrium, two-dimensional superfluid near the critical point, the energy for dissipative fluctuations is greatly reduced as a result of screening by the gas of bound vortex pairs, leading to an enhanced decay of the superfluid velocity. We also show that the superfluid density is reduced by a velocity-dependent amount as $T_c$ is approached from below.

• Received 17 November 1977

DOI:https://doi.org/10.1103/PhysRevLett.40.780