Resonant-Subband Landau-Level Coupling in a Two-Dimensional Electronic System: Depolarization Effect and Dependence on Carrier Density

Abstract

For a quantitative understanding of the properties of a two-dimensional electron gas the exact knowledge of subband energies and wavefunctions is very important [1].Experimentally one usually applies optical techniques such as Raman scattering [2,3] and resonant-subband-Landau-level-coupling (RSLC) spectroscopy [4–6]. Using Raman scattering the presence of strong bandgap radiation causes quasi-accumulation conditions and fixes the two-dimensional (2D) carrier density Ns. So far RSLC was investigated as a function of bandgap illumination [5,6] or back-gate voltage [5], which both strongly influence the depletion charge N depl of an Al x Ga 1−x As - GaAs heterostructure. In particular it was not clear whether the energies, determined from RSLC experiments, are depolarization shifted as in charge density excitation experiments [3]. Therefore it was difficult to compare experiments and results of self-consistent calculations [7,8] in a satisfactory manner Here we prepared modulation doped Al x Ga 1−x As - GaAs heterostructures with front-gates which allowed us to change N, in a controlled and reproducible way [9,10] .This gave us the possibility to study RSLC as a function of Ns,while all other parameters remained essentially unchanged. The agreement between our experimental results and a self-consistent calculation is excellent and clearly reveals that the energies, determined from RSLC experiments, are depolarization shifted.