We study the many-body effects in a two-subband quasi-two-dimensional electron system in a quantizing magnetic field at filling factor three. A manifestation of these effects in the phonon absorption spectroscopy is discussed. The electron system is mapped onto a two-level system with the separation between levels determined by the intersubband splitting and the cyclotron energy. The electron-electron interaction enhances the excitation gap, which exists at all values of the interlevel splitting. This results in a single-peak structure of the phonon absorption rate as a function of magnetic field, instead of the double-peak structure for non-interacting electrons. © 2002 Elsevier Science B.V. All rights reserved.
Apalkov, V. M., & Portnoi, M. E. (2002). Two-subband system in quantizing magnetic field: Probing many-body gap by non-equilibrium phonons. Physica E: Low-Dimensional Systems and Nanostructures, 15(3), 202–210. https://doi.org/10.1016/S1386-9477(02)00554-4