Quantized phase slippage in superfluidHe4

Abstract

We have studied dissipative phase-slip events in the oscillatory superflow of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ through two different orifices of submicron size. The dissipation events are found to be caused by the phase difference across the orifice changing by 2πn, where the slip integer n depends on the orifice geometry, flow direction, and temperature. The temperature dependence of the phase-slip critical velocity indicates that surface microstructure determines the magnitude of relevant energy barriers.