Far Infrared Cyclotron Reasonance in Metals

The authors observed cyclotron resonance in copper at four frequencies (29.69, 32.12, 45.407, and 58.25/cm) as well as at microwave frequency (2.4/cm). 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.