Interfacial pinning in the superfluid 3He A-B transition in aerogel.

Continuous-wave NMR studies of 3He in the presence of 99.3% porosity silica aerogel at 34.0 bars and in a magnetic field of 28.4 mT reveal a first-order phase transition between A-like and B-like superfluid phases on both warming and cooling. NMR spectra show that the phases on warming are the same as the phases on cooling, and the interface between them is found to be strongly pinned, even close to T(c,aero). The observed behavior is consistent with spatial variation of pinning strengths within the aerogel.