Phonon Cyclotron Resonance in the Infrared Absorption inn-Type InSb

Abstract

A series of peaks has been observed in the infrared absorption by free carriers in $n$-type InSb under applied magnetic field. With decreasing field, the peaks converge to an energy equal to that of a LO phonon. The energy separations between the peaks are related to the separations of Landau levels. These peaks are called phonon cyclotron resonances, and they are associated with indirect transitions involving LO phonons. A theory is presented which accounts for various aspects of the observation including the positions and the strengths of the resonances as well as the effect of polarization on the resonances. Some peaks were observed in addition to the phonon cyclotron resonances, which appear to represent the third harmonic of cyclotron resonance and the second harmonic with spin flip.