Far Infrared Cyclotron Reasonance in Metals.

The authors observed cyclotron resonance in copper at four frequencies 29.69, 32.12, 45.407, and 58.25cm as well as at microwave frequency 2.4cm. Similar experiments in lead yielded no observable resonances, which set an upper bound on the signal strength at far infrared frequencies. These experiments were performed on a calorimetric spectrometer and a reflection cavity spectrometer. The observed lineshapes in copper have been analyzed with various calculations of the surface impedance change at resonance. The first calculation makes a spherical approximation for the Fermi surface and includes the effects of retardation and high frequency cyclotron wave propagation due to a large resonant conductivity. Another surface impedance calculation was then performed which takes into account also the Fermi surface anisotropy.