Attenuation of zero sound and the several low-temperature phases of liquid3He
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Measurements of the attenuation of 10-MHz compressional waves in liquid3He along the melting curve reveal a sharp peak at the A transition (2.7 mK). In a magnetic field this feature splits into two attenuation peaks, separated by a temperature difference proportional to H. The shapes of these peaks, though changing markedly between H=0 and 1 kOe, are all consistent with the A phase being an anisotropic BCS-type superfluid and inconsistent with an isotropic gap model. Field-dependent time variations in the attenuation and various transient effects provide further clues to the nature of this phase. A third sharp attenuation peak-at the B transition (2 mK)-possibly represents scattering from a liquid-liquid interface. It is, in any event, consistent with an isotropic superfluid B phase. Velocity changes have been observed at both A and B transitions, indicating velocities in the B phase significantly less than that of first sound at the same pressure. 1974 Plenum Publishing Corporation.