title: Critical velocity of continuous vortex nucleation in a slab of superfluid 3He-A.
abstract: A flow-induced Fréedericksz transition is observed in a 0.26 mm thick disk-shaped slab of superfluid 3He-A using a rotating cryostat and a torsional oscillator, and it is used to detect vortices in zero magnetic field. The phenomena are studied as a function of magnetic field normal to the slab. In defect-free l texture the critical velocity for vortex nucleation is 0.5 mm/s, but in the presence of a domain wall it is reduced to approximately Planck's over 2pi /2ma(c), where a(c)(H) is the field-dependent radius of the vortex soft core. The vortices nucleate at a distance at least 0.3 mm from the outer edge of the disk.
authors.affiliation: Department of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, United Kingdom.
authors.forename: P M
authors.initials: PM
authors.lastname: Walmsley
authors.forename: D J
authors.initials: DJ
authors.lastname: Cousins
authors.forename: A I
authors.initials: AI
authors.lastname: Golov