COLLECTIVE CYCLOTRON MODES IN HIGH-MOBILITY 2-DIMENSIONAL HOLE SYSTEMS IN GAAS-(GA,AL)AS HETEROJUNCTIONS .1. EXPERIMENTS AT LOW MAGNETIC-FIELDS AND THEORY

The cyclotron resonance of very high-mobility two-dimensional holes in GaAs-(Ga, AI)As heterojunctions grown on (111), (311) and (100) subst rates has been studied over the frequency range 30 to 200 GHz. Althoug h the presence of two hole spin subbands in the samples suggests that two cyclotron resonances should be observed, in practice only a single resonance occurs for a wide range of conditions (temperature, field) and sample properties (hole density, mobility). Furthermore, the cyclo tron resonance spectra often exhibit a strong temperature dependence. In the case of a single, sharp cyclotron resonance, the resonance held may shift by as much as 20% when warming the sample from 1.4 to 4.2 K . In the case of spectra containing multiple cyclotron resonances, sim ilar changes in temperature shift the resonance positions together to form a single cyclotron absorption. This behaviour is explained in ter ms of two interacting hole subsystems with different effective masses formed by the two spin subbands. An analytical expression for the cont ribution to the high-frequency conductivity due to coupled cyclotron m otion of the two hole systems is derived and shown to encompass previo us theories developed for more restricted ranges of conditions. The ex pression predicts the complex behaviour of the experimental spectra ve ry well, and enables hole masses, hole-lattice scattering rates and ho le-hole scattering rates to be extracted. Comparisons between theory a nd data also show that a reactive interaction dominates the coupling b etween the spin subsystems at low temperatures. This is the first of t wo papers dealing with correlated hole cyclotron resonance; the second shows that the model derived in this work can also be used to treat c yclotron resonance data recorded at very high magnetic fields similar to 40 T.