Modification of the superfluid 3He phase diagram by impurity scattering

The effect of impurity scattering on the phase diagram of pure superfluid 3He has been investigated by acoustic techniques near the bulk polycritical pressure. Impurities were introduced with a 98% porous silica aerogel. In zero applied field, the equilibrium phase is a B phase, consistent with predictions from isotropic scattering. The superfluid transition in a magnetic field at 25 bars is from normal to A phase and is independent of the magnetic field up to 2.9 kG. A first-order phase transition between A and B superfluids is observed with surprisingly strong supercooling in both zero and nonzero applied field.