Ultrasonic attenuation in normal and superconducting indium

Abstract

Measurements were made of the variation of ultrasonic attenuation in indium between 4.2 °K and 1.3 °K for longitudinal waves at 50 Mc/s and 90 Mc/s and for transverse waves at 50 Mc/s. The results were analysed to determine the electronic contribution to the total attenuation. Low-amplitude dislocation attenuation was significant. Amplitude-dependent attenuation was investigated qualitatively. The electronic attenuation and the electronic mean free path were very anisotropic. The transverse normal-state attenuation decreased with decreasing temperature, in spite of the increasing mean free path. The results are discussed in terms of a suggested mean free path reduction near the edges of the Fermi surface in the reduced-zone scheme. The anisotropies are attributed to the combination of a sharply peaked electronic distribution function under the action of the ultrasonic wave, a Fermi surface with sharp edges, and a high probability of small-momentum scattering by thermal phonons For propagation along [110] the value of the average deformation parameter Kx is calculated to be equal to the free-electron value. For propagation normal to (111) Kx is 26% greater than this value. These results, together with the large observed transverse attenuation in the superconducting state, indicate that band structure effects on the deformation parameters for indium are appreciable.