Theory of nonlinear cyclotron resonance in quasi-two-dimensional electron systems

Momentum-and energy-balance equations are developed for steady-state electron transport and optical absorption under the influence of a dc electric field and an intense ac electric field of terahertz (THz) frequency in a two-dimensional (2D) semiconductor in the presence of a strong magnetic field perpendicular to the 2D plane. These equations are applied to study the intensity-dependent cyclotron resonance (CR) in far-infrared transmission and THz-radiation-induced photoconductivity of GaAs heterostructures in the Faraday geometry. We find that the CR peaks and line shapes of the transmittance exhibit different intensity dependences when the intensity of the THz field increases in the ranges above or below a certain critical value. The CR in the photoresistivity, however, is always enhanced on increasing the intensity of the THz field. These results agree qualitatively with the experimental observations. We have clarified that the CR in the photoconductivity is not only a result of the electron heating, but also arises from photon-assisted scattering enhancement, especially at high temperatures. The effects of an intense THz field on the Faraday angle and ellipticity of magnetically biased 2D semiconductors have also been demonstrated.