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

摘要

Phase transition in superfluid ~(3)He 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 T_(c)~(aero) to the lowest temperature of coexistence, T_(AB~(aero)), 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 (mu)K wide, the upper region being just below T_(c~(aero)) and the lower one just above T_(AB~(aero)). 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.