CREATION OF QUANTIZED VORTICES AT THE LAMBDA-TRANSITION IN LIQUID-HE-4

A fast (approximately 3 ms) adiabatic expansion of a volume of liquid He-4 through the lambda transition is being used to study the nature o f the transition and to model the cosmological false vacuum to true va cuum phase transition of the early universe. Preliminary results are r eported showing that, in accordance with theoretical predictions by W H Zurek (Nature 317, 505; 1985), there is copious production of quanti zed vortex lines, which represent the superfluid analogue of cosmic st rings. The line density after the expansion appears to decay in two di stinct stages, with a fast decay being followed by a much slower one, in agreement with earlier work on the decay of quantum turbulence crea ted in thermal counterflow. Extrapolation of the initial fast decay su ggests an initial line density, immediately following the expansion, o f approximately 10(7) cm-2. Smaller, but still substantial, vortex den sities are also found to occur when the system is expanded from below the lambda transition, and the physical implications are discussed.