Nucleation of the ab transition in superfluid ³he: Experimental and theoretical considerations

The A and B phases of superfluid ³He are generally believed to correspond to two p-wave BCS states known as the ABM and the BW states, respectively. This chapter describes the progress made in understanding the unique properties of AB transition. The primary conclusion that can be drawn from the Stanford experiments is ionizing radiation that leads to the nucleation of the B phase in superfluid ³helium (He). The nucleation rate increases by more than three orders of magnitude when the source is placed nearby. In the absence of radiation, the singularity known as a “boojum” potentially result in a B phase nucleation rate close to that observed experimentally in conventional cells. Lower pressure experiments have the advantage of shorter thermal relaxation times because of the higher thermal conductivity and lower heat capacity at lower pressures and because of the smaller temperature ranges through which the samples need to be cycled to “reset” the phase between runs.