Electron Viscosity and Ultrasonic Attenuation in Noble Metals

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Abstract
Low-temperature absolute ultrasonic attenuations have been observed in silver and copper which are higher than free-electron predictions by a factor of 1.8. Since the real Fermi surfaces of the noble metals are now well enough known to be taken into account, we have formulated expressions for the viscosity tensor of a nonisotropic Bloch electron gas and, in a relaxation-time approximation, deduced detailed formulas for the case of the metals Ag, Au, and Cu, which conform to cubic symmetry. The nondynamical deviations from spherical symmetry do not account for the high observed attenuations, but they do create a marked anisotropy in the viscosity tensor. The electron deformation potential probably contributes significantly.

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