Sound Attenuation Measurements in SuperfluidHe3-AWell belowTc: An Anomalous Behavior at Low Pressure

Abstract
Sound attenuation has been measured at low and medium pressures down to TTc0.4 in the A phase of superfluid He3 stabilized by a magnetic field. Damping is due to Cooper pair breaking and constitutes a useful probe of the superfluid gap. The gap parameter is found to correspond to the weak-coupling value at high pressure but to be anomalously small at low pressure.