Cyclotron Resonance in Aluminum

Abstract

A systematic study of Azbel'-Kaner cyclotron resonance in aluminum at 35 Gc/sec has clarified and extended previous work. Results on the orientation dependence and relative values of the cyclotron mass for different electron orbits correspond closely with expectations based on Harrison's free-electron model. However, the observed mass values are consistently 55-60% higher than those predicted by the free-electron model. Since the nearly-free-electron model agrees with ab initio band-structure calculations which exist for aluminum and which are thought to be reliable within the independent-particle model, the bulk of this discrepancy is presumed to be attributable to the many-body effects of correlation and electron-phonon interactions. The anomalous cyclotron resonance spectrum attributed in previous work to a cyclotron mass of $3.10m$ ($m$ is the free electron mass) is elucidated in terms of current sheets which reproduce the skin currents deep within the metal. These sheets are produced by the spatially periodic magnetic focusing of limiting-point electrons on the Fermi surface. This mechanism leads to a cyclotron mass for these electrons of $1.55m$, just one half the value given on the Azbel'-Kaner model. Quantum oscillations in the surface impedance analogous to the de Haas-van Alphen oscillations in the susceptibility are observed at ∼1.5°K. Observed periods agree with the de Haas-van Alphen periods measured by Gunnersen.