The excitations of a two-dimensional electron gas in quantum wells with intermediate carrier density (ne ∼ 1011 cm−2), i.e., between the exciton-trion and the Fermi-sea range, are so far poorly understood. We report on an approach to bridge this gap by a magnetophotoluminescence study of modulation-doped (Cd,Mn)Te quantum well structures. Employing their enhanced spin splitting, we analyzed the characteristic magnetic-field behavior of the individual photoluminescence features. Based on these results and earlier findings by other authors, we present a new approach for understanding the optical transitions at intermediate densities in terms of four-particle excitations, the Suris tetrons, which were up to now only predicted theoretically. All characteristic photoluminescence features are attributed to emission from these quasiparticles when attaining different final states.
Koudinov, A. V., Kehl, C., Rodina, A. V., Geurts, J., Wolverson, D., & Karczewski, G. (2014). Suris tetrons: possible spectroscopic evidence for four-particle optical excitations of a two-dimensional electron gas. Physical Review Letters, 112(14), 1-5. . https://doi.org/10.1103/PhysRevLett.112.147402