Cyclotron resonance and spin states in GaAs/Ga1-xAlxAs heterojunctions: Experiment and theory

The cyclotron resonance of high-mobility GaAs/AlxGa1-xAs heterojunctions displays both a temperature and Landau-level occupancy nu dependence. For occupancies below similar to 1/10, the behavior is identical to that found in high-purity bulk GaAs with spin splitting of the resonance. The position of the two peaks changes only slightly as the temperature is raised from 0.1 to 2 K. For 1/10 less than or equal to nu less than or equal to 1/6, the peak position and relative peak intensity of the two peaks shifts radically as the temperature is raised or the density varied. At integral and greater occupancies only a single cyclotron resonance peak is observed whose position changes very little with temperature. Finally, the fractional regime with occupancies between 1/6 and 1 shows only a single cyclotron resonance with a slight temperature dependence and provides no evidence that the many-body interactions responsible for the fractional quantum Hall effect influence the cyclotron resonance. The experimental cyclotron resonance behavior can be explained by a recently published theory by Cooper and Chalker which models the system in terms of the Coulomb interaction and the thermal population of both spin slates. A rigorous comparison between data taken over a wide range of densities and temperatures and the theoretical model establishes the validity of this explanation.