We have determined the features of a universal energy barrier which mediates the thermal nucleation of quantized vortices. The barrier is deduced from measurements of the intrinsic phase slip critical velocity using both dc flow and single phase slip experiments. It appears that at a given temperature a single curve can predict the outcome of all intrinsic vortex nucleation experiments for flow through small apertures.

• Received 15 February 1995

DOI:https://doi.org/10.1103/PhysRevLett.74.5056