In pure liquid 4He, my work has included the study of persistent superfluid flow, the quantization of superfluid circulation, the trapping of ions by superfluid vortices, the superfluid critical velocity and the alteration of the superfluid density in fine pores near the lambda transition, and superfluid vortex generation in flow through orifices of submicron size. My work has also included the study of some of these same effects in superfluid 3He/4He mixtures, measurements of the heat capacity and concentration susceptibility of these mixtures near the tricritical point, and studies of the thin superfluid film that forms on the walls of a vessel containing the normal phase of the mixtures near the tricritical point.
Currently, I am investigating the effect of applying large electric fields to superfluid 4He near the lambda transition. Such fields are being applied to the helium in the pores of membranes that are being used to generate and detect second sound in the liquid. The fields are observed to affect the efficiency with which the membranes generate and respond to second sound at temperatures of a few tenths of a millikelvin below the lambda temperature.
