First-Sound Attenuation and Viscosity of SuperfluidHe3-B

Abstract

The attenuation of first sound in normal and superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in a cylindrical resonator has been measured from 40 kHz to 300 kHz at 8 and 28 bars. In the $B$ phase a decreasing viscosity down to the lowest temperature ($0.5T_c$) is observed. In the normal phase the viscosity agrees with previously reported values. The data analysis is based on a recent theory of sound propagation in superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ in a resonator.