The influence of inter-subband interactions and self-consistent effects on the magnetotransport in GaAs-(Ga,Al) as heterojunctions with two populated subbands

Abstract

A phenomenological model of the Shubnikov-de Haas (SdH) oscillations of 2-Dimensional Electron Gases (2DEG's) with two or more populated subbands is applied to our experimental data from high-mobility GaAs-(Ga,Al)As heterojunctions with two populated subbands. The model assumes Gaussian broadened Landau levels, plus a background density of localised states: other density of states functions may be also chosen. The agreements and discrepancies between the model calculations and experimental data are discussed and the importance of self-consistent effects, such as g-factor enhancement, oscillatory screening and non-linear intersubband scattering is indicated qualitatively. These effects can be incorporated into the model in a phenomenological manner to give a rather good fit to the experimental data: in this manner information on the actual density of states can be inferred. Further information on the influence of the second subband has been gained from magnetoresistance measurements performed in parallel-field (i.e. magnetic field in the plane of the 2DEG) and near parallel-field orientations. These experiments show that when the second subband becomes populated, there is a decrease of the level broadening in the lower subband due to screening by the second subband, accompanied by a decrease of the transport mobility due to the onset of intersubband scattering.