Collective cyclotron modes in high-mobility two-dimensional hole systems in GaAs - (Ga, Al)As heterojunctions: I. Experiments at low magnetic fields and theory

Abstract

The cyclotron resonance of very high-mobility two-dimensional holes in GaAs - (Ga, Al)As heterojunctions grown on (111), (311) and (100) substrates has been studied over the frequency range 30 to 200 GHz. Although 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 cyclotron resonance spectra often exhibit a strong temperature dependence. In the case of a single, sharp cyclotron resonance, the resonance field 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, similar changes in temperature shift the resonance positions together to form a single cyclotron absorption. This behaviour is explained in terms of two interacting hole subsystems with different effective masses formed by the two spin subbands. An analytical expression for the contribution to the high-frequency conductivity due to coupled cyclotron motion of the two hole systems is derived and shown to encompass previous theories developed for more restricted ranges of conditions. The expression predicts the complex behaviour of the experimental spectra very well, and enables hole masses, hole - lattice scattering rates and hole - hole scattering rates to be extracted. Comparisons between theory and data also show that a reactive interaction dominates the coupling between the spin subsystems at low temperatures. This is the first of two papers dealing with correlated hole cyclotron resonance; the second shows that the model derived in this work can also be used to treat cyclotron resonance data recorded at very high magnetic fields .

Cyclotron resonance of carbon-doped two-dimensional hole systems: From the magnetic quantum limit to low magnetic fields

“…[5][6][7][8][9][10][11][12][13][14] At first, 2DHSs in Si-metal-oxidesemiconductor ͑MOS͒ structures were investigated. 5 The first CR experiments on GaAs-based 2DHS were performed on Be-doped ͑100͒ samples.…”

“…Other publications dealt with the influence of carrier-carrier interactions on the spin-split CRs. 13 Here, a two-level system was assumed at sufficient low B; thus, that the nonparabolicity did not play an essential role.…”

Blocking of the Polaron Effect and Spin-Split Cyclotron Resonance in a Two-Dimensional Electron Gas

“…Within the approximation of frequency independent electron-electron scattering time, the relaxation of the relative total momentum P is governed by dP͞dt M e ͑v͒P ͑iv e 2 1͞t e ͒P. This model has been well studied, where v e shifts the CR frequencies, while t e broadens the CR peaks [19][20][21]. Such a study indicated that we are in the weak electron-electron coupling regime with almost no mixing of the two modes.…”

“…It is clear that there are two CR peaks in general, and the size of the splitting is determined by the memory function. The electron-electron interaction can couple these two CR transitions [6,7,[19][20][21] producing a single mode or two mixed modes.…”

“…This is so below the reststrahlen region, and also above the reststrahlen region when the ratio between the occupancy of the two spin states is close to 1. Another reason can be that the electron-electron interaction couples the two CR transitions which may lead to a single mode as was found in previous CR studies [5,6,[19][20][21]. We considered the influence of electron-electron interaction phenomenologically along the lines of [19][20][21], which is equivalent to that used in [5,6,11,12].…”