Interaction of above-Fermi-edge magnetoexciton states from different subbands in dense two-dimensional electron magnetoplasma

Photoluminescence spectra from δ-doped n-type ${\mathrm{Al}}_{\mathit{y}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{y}}$As/${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ga}}_{\mathit{x}}$As/GaAs quantum wells have been investigated in magnetic fields H≤14 T and T=1.8–18 K. The Fermi level of the quasi-two-dimensional electron gas ${\mathit{E}}_{\mathit{F}}$ was slightly below the second subband. Interband Landau-level (LL) transitions between the ${\mathit{j}}_{\mathit{e}}$th electron LL (${\mathit{j}}_{\mathit{e}}$=1,2) and the first hole LL, ${\mathit{j}}_{\mathit{e}\mathrm{-}}$ $1_{\mathit{h}}$, were analyzed. Their intensity was found to increase anomalously when the transition energy intersected that of the magnetoexciton state involving the electron from the second subband, $0_{\mathit{e}}^{2\mathrm{-}}$ $0_{\mathit{h}}$. The intensity of the $0_{\mathit{e}}^{2\mathrm{-}}$ $0_{\mathit{h}}$ line oscillated with magnetic field and its maxima coincided with the intersection between the $0_{\mathit{e}}^{2\mathrm{-}}$ $0_{\mathit{h}}$ energy and either the ${\mathit{j}}_{\mathit{e}\mathrm{-}}$ $0_{\mathit{h}}$ or ${\mathit{j}}_{\mathit{e}\mathrm{-}}$ $1_{\mathit{h}}$ transitions or both of them, depending on the energy separation between ${\mathit{E}}_{\mathit{F}}$ and the second subband. Taking into account that the ${\mathit{j}}_{\mathit{e}\mathrm{-}}$ $1_{\mathit{h}}$ and $0_{\mathit{e}}^{2\mathrm{-}}$ $0_{\mathit{h}}$ transitions involve no common particle, the anomalous behavior is explained by the interaction between two magnetoexciton states, $0_{\mathit{e}}^{2\mathrm{-}}$ $0_{\mathit{h}}$ and ${\mathit{j}}_{\mathit{e}\mathrm{-}}$ $1_{\mathit{h}}$.