We use a phenomenological theory of superfluid critical velocities in small orifices to explain three phenomena: (1) The low-temperature intrinsic critical velocity in dc experiments should depend logarithmically on the driving pressure head; the logarithmic increment in is the width of the velocity distribution function for phase slips. (2) The critical velocity measured in dc experiments is related to that seen in ac experiments through the quantum number of the phase slips involved. (3) It is possible that quantum tunneling processes may be significant at temperatures as high as 0.3 K.
- Received 9 September 1991
- Published in the issue dated 1 February 1992
© 1992 The American Physical Society