Superfluid 3He in strong magnetic fields: Anomalous sound attenuation in the B phase and evidence for splitting of the AB transition.

Abstract

Zero sound attenuation at 8.9 and 26.8 MHz in {sup 3}He-{ital B} shows an extremum at {ital T}{sub {ital AB}} in a field of {approx}2 kG at low pressures, both in the stationary and in the rotating superfluid. This is in accordance with the prediction that a critical magnetic field separates two types of {ital B} phases at the {ital AB} transition line, with and without nodes in the energy gap, respectively, and with a change in the nature of the transition. The {ital AB} phase transition takes place via an intermediate state, possibly a new phase, characterized by excess sound attenuation.