Pair-breaking edge of superfluid 3He-B in a magnetic field

We have conducted ultrasound pulse transmission experiments to investigate the pair-breaking edge for superfluid 3He-B in a magnetic field. The experiments were performed at 3He temperatures below 0.4Tc, pressures between 6 and 29.3 bars, and ultrasound frequencies of 168.33, 137.6, and 107 MHz. We used both depressurization and demagnetization techniques to measure the linear and quadratic magnetic field dependence of the pair-breaking edge frequency. We obtain values for the Fermi-liquid interaction parameter F2a from the coefficient of the linear term. The quadratic term is due to the energy-gap distortion and its value is consistent with calculations of Schopohl and Tewordt