On the moving A-B phase boundary of superfluid 3He

We investigate the A-B phase boundary of superfluid 3He at very low temperatures under near-equilibrium conditions where it expands with uniform velocity ν into the undercooled A phase. Neglecting collisions between excitations, essentially exact solutions to the 'microscopic' Gorkov equations are found that describe fermionic excitations which scatter from the moving interface. The distribution function of such fermions is characterized by an essential singularity at ν = O and translates rigidly with the A-B phase boundary only below a critical speed νcl. (author)