CYCLOTRON-RESONANCE AND SPIN STATES IN GAAS GA1-XALXAS HETEROJUNCTIONS - EXPERIMENT AND THEORY/

The cyclotron resonance of high-mobility GaAs/AlxGa1-xAs heterojunctio ns displays both a temperature and Landau-level occupancy nu dependenc e. For occupancies below similar to 1/10, the behavior is identical to that found in high-purity bulk GaAs with spin splitting of the resona nce. The position of the two peaks changes only slightly as the temper ature is raised from 0.1 to 2 K. For 1/10 less than or equal to nu les s 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 cycl otron resonance peak is observed whose position changes very little wi th temperature. Finally, the fractional regime with occupancies betwee n 1/6 and 1 shows only a single cyclotron resonance with a slight temp erature dependence and provides no evidence that the many-body interac tions responsible for the fractional quantum Hall effect influence the cyclotron resonance. The experimental cyclotron resonance behavior ca n be explained by a recently published theory by Cooper and Chalker wh ich models the system in terms of the Coulomb interaction and the ther mal population of both spin slates. A rigorous comparison between data taken over a wide range of densities and temperatures and the theoret ical model establishes the validity of this explanation.