A-B Phase Transition and Pinning of Phase Boundary of Superfluid 3He in Aerogel

Phase transition in superfluid 3He in aerogel has been studied by NMR. Above 19 bar, we have clearly observed the A-like and B-like phases by following changes in the NMR lineshapes and resonance frequencies. There is a wide temperature region in which the A-like phase and the B-like phase coexist, extending from near the superfluid transition temperature Tcaero to the lowest temperature of coexistence, TABaero, below which only the B-like phase exists. There are two temperature regions, only in which the phase conversion occurs. Both regions are a few tens of μK wide, the upper region being just below Tcaero and the lower one just above TABaero. In cooling down and warming up with the two phases in coexistence, no phase conversion occurs between the two regions. The phase boundary between the A-like phase and B-like phase cannot move in aerogel due to strong pinning by inhomogenities of aerogel