Search For New Superfluid States Of 3He Confined In Coherence Length Sized Nanofabricated Structures
Properties of superfluid 3 He are greatly affected by proximity of surfaces and disorder. In this work, we describe three different experiments for which we use torsion pendulums to study the properties of the 3 He fluid confined within the torsion pendulum heads. In the first two experiments, the fluid was embedded within anisotropic aerogel samples. In one case, we compressed an otherwise isotropic 98% open silica aerogel. In the other, we used a highly oriented, "nematically ordered" aerogel sample, which represented the limit of extremely stretched aerogel. In the third experiment, 3 He was confined within a nanofabricated high aspect ration 1080 nm deep cavity formed between patterned silicon disc bonded to a matching glass piece. We obtained data for the superfluid fraction versus temperature for a number of pressures. We observe great modifications of the superfluid phase diagram for the confined fluid in all three experiments. The order parameters for the A and B phases are distorted and the regions of stability for these phases is drastically different compared to the bulk or previous experiments with isotropic aerogels. In particular, the highly anisotropic disorder provided by the "nematically ordered" aerogel sample gives rise to a phase transition not seen in the bulk. We argue that at low pressures in the temperature region near the superfluid transition we observe a superfluid state that is closely related to Polar phase. In the experiment in which we confined the fluid within the 1080 nm deep cavity, we see an A to B phase transition at all experimental pressures. We, however, do not observe any signature of a new superfluid state (Stripe phase), which has been predicted to occur at the onset of the A to B transition.
superfluid helium-3; aerogels; thin films
Mueller,Erich; Davis,James C.
Ph. D., Physics
Doctor of Philosophy
dissertation or thesis