Nucleation and Interfacial Coupling between Pure and Dirty Superfluid Phases of 3He

The nucleation of the first order phase transition of superfluid 3He-B from superfluid 3He-A is quite remarkable since it requires a seed of the order of a micron. We have studied this nucleation for 3He confined to a very dilute silica aerogel. This dirty superfluid behaves in a manner similar to previous reports for the pure superfluid. But we have discovered a novel magnetically driven nucleation switch acting on the pure superfluid B-phase. Lastly, we find the surprising result that the proximity effect between the pure and dirty superfluids at their interface is insufficient to nucleate the B-phase in either superfluid.
4 pages, 4 figures, to be published in Physical Review Letters