Elastic Constants of bccHe3from Measurements of Sound Velocity, Debye Temperature, and Compressibility

Abstract

In single crystals with the large anisotropy of bcc ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ the wave vector of a sound wave deviates as much as 60° from the direction of energy flow. This effect permits one to find single-crystal elastic constants from previous measurements of the transverse velocity, the Debye temperature and the compressibility: $c_{11}=2.35\mathrm{}$, $c_{12}=1.97\mathrm{}$, $c_{44}=1.085\mathrm{}$ (in ${10}^8$ dyn/${\mathrm{cm}}^2$) at a molar volume of 24 ${\mathrm{cm}}^3$/mole. The constants agree well with measured longitudinal sound velocities and with theoretical constants of Horner, less well with constants obtained from the single-particle theories of Nosanow et al.