Attenuation of First Sound Near the Lambda Transition of Liquid Helium

Abstract

The attenuation of first sound near the lambda point can be interpreted as being due to two phenomena: (1) a relaxation process described by Pokrovskii and Khalatnikov occurring only below the lambda point, and having a relaxation time of $\frac{\xi }{C_2}$ where $C_2$ is the velocity of second sound and $\xi$ is a coherence length of magnitude $1.36\times {10}^{-8\mathrm{}}{(T_{\lambda }-T)}^{\frac{-2\mathrm{}}{3}}$ cm; (2) a critical attenuation which is nonsingular and symmetrical about $T_{\lambda }$.