Second-Sound Velocities in Cubic Crystals

Abstract

Accurate values of "drifting" and "driftless" second sound at 0 K are obtained for alkalihalide crystals and ten other cubic crystals. The percentage difference between the two types of second sound is found to vary from 3.8 to 16.2%. The ratio $R=\frac{〈v^2〉}{3v_{\mathrm{II}}^2}$, where $v$ is the sound velocity and $v_{\mathrm{II}}$ is the drifting second-sound velocity, is also studied and is shown to be correlated with the degree of anisotropy of the substance.