ANISOTROPIC ATTENUATION OF ZERO SOUND IN SUPERFLUID HE-3-A

The anisotropic attenuation of zero sound in superfluid3He-A at 29.3 bar pressure has been measured at 24.4, 34.2, 44.2, 54.0, 63.9, 73.7, 83.5, and 93.4 MHz. The clapping mode resonance has been observed at all frequencies, and the reentrant normal flapping resonance has been measured for the first time. Analysis of these results leads to an f-wave pairing parameter, x3-1-0.1±0.05, and a determination of strong coupling corrections to the energy gap far from Tc. This is expressed by an enhancement of the zero-temperature energy gap by a factor 1.3±0.1 above that of weak coupling, 2.03 kBTc. The clapping mode data is consistent with a nontrivial, strong coupling correction to the mode frequency, reducing it by 6%. The3He was confined to a slab 250 μm in thickness and the superfluid texture was oriented by a magnetic field. This allowed attenuations up to 100 cm-1 to be resolved and the attenuation from pair-breaking processes alone to be determined for the first time. The sound attenuation was measured for angles between the sound propagation direction and the 1vector of 0, π/4, and π/2. The sensitivity of the numerically evaluated attenuation to quasiparticle collision time, f-wave parameter, and uniformity of the orbital texture is explored. © 1990 Plenum Publishing Corporation.