Attenuation and Rotation of Plane-Polarized Ultrasound in Copper in a Longitudinal Magnetic Field

The rotation of the plane of polarization and attenuation of a shear sound wave at 4.2^∘{}K have been measured for the propagation vector q parallel to the magnetic field B in the [001] direction in copper. Frequencies from 30 to 110 Mc/sec were used. Both the attenuation and rotation are periodic in νB, where ν is the sound frequency. The period for the attenuation is 0.0201±{}0.0005 Mc/sec G, whereas the period for the rotation is 0.0402±{}0.001 Mc/sec G. A. theory is presented which describes this effect. The oscillations in the attenuation are of the type predicted by Kaner, Peschanskii, and Privorotskii, with a peak in the attenuation preceding an absorption edge. An absorption edge is observed at about one-fourth the magnetic field value expected for the free-electron case. The results are interpreted in terms of the Fermi surface of copper as put forth by Roaf. A method is suggested for determining ωcτ, where ωc is the cyclotron frequency and τ the relaxation time; a value of mcv̄z=0.381±0.009×10^-19 g cm/sec is assigned to electrons with orbits near the plane kz=0.45×10⁸ cm^-1, where mc is the cyclotron effective mass, v̄z is the drift velocity, and kz is the [001] direction.