Attenuation of zero sound in oriented liquid 3He-A

Systematic measurements of the change α-α/sub c/ of the absorption coefficient for zero sound in 3He-A from its value at T/sub c/ are presented for both 24.08 and 33.53 bar and several frequencies. The 3He-A is oriented by means of a magnetic field, so only the case where field and sound directions are parallel give results which can be reliably compared with theory. We find that for 5-MHz zero sound at temperatures well below the collective modes peak there is a substantial anisotropy of the attenuation. We also find at high enough frequency a linear relationship between the sonic frequency and the location on a (1-T/T/sub c/)1/2 scale of the collective modes peak for lxq=0. Comparison of theory and experiment for these data is excellent and suggests that the method may be an accurate one for measuring the temperature dependence of the energy gap in 3He-A