We report observations of the decay of persistent currents of thin superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ films for which the superfluid velocity deviates strongly from the previously observed $logt$ behavior. We present data which document the evolution of this behavior as a function of film thickness. The Iordanskii-Langer-Fisher theory does not accurately describe our observations.

• Received 27 November 1978

DOI:https://doi.org/10.1103/PhysRevLett.42.449