Suppression of the critical current and transition temperature of superfluid ³he in a single submicron cylindrical channel

The flow of superfluid ³He through a single cylindrical channel of 0.7 micron diameter is studied. suppresion of the transition temperature and of the depairing critical current density are observed indicating that the boundary condition at the wall is that for diffuse quasiparticle scattering. The suppresions agree reasonably well with model calculations for this geometry using the diffuse scattering boundary conditions. Some evidence for dissipation of superflow due to thermal activation of 2π phase slips of the order parameter inside the channel is seen.