Ultrasonic Investigation of Open Orbits in Cadmium and Zinc

An experimental investigation of the frequency and temperature variation of ultrasonic resonance absorption by open-orbit electrons moving parallel to [0001] in Cd and Zn is presented. The observations indicate conclusively that the Fermi surfaces of Cd and Zn are open parallel to [0001]. The Brillouin zone dimensions along [0001] calculated from the experimental data are 1.20±0.005×${10}^{-19\mathrm{}}$ g cm/sec for Cd and 1.36±0.01 ×${10}^{-19\mathrm{}}$ g cm/sec for Zn. These values agree very well with x-ray data and provide experimental evidence against the possibility of there being an effective charge carrier $e^{*}$ different from the electronic charge $e$. The frequency dependence of the resonance is found to agree quite well with theory, and no evidence for magnetic breakdown is seen up to 2000 G. The width of the open-orbit resonance is directly related to the electron mean free path $l$, thus allowing a determination of $l$ for the open-orbit electrons from sample to sample or as the temperature varies in a particular sample.