Direct observation of magnetoplasmon-phonon coupled modes in the magnetophotoluminescence spectra of the two-dimensional electron gas in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs quantum wells

Novel well-resolved emission lines in the spectral range of phonon replicas were observed in low-temperature magnetoluminescence spectra of the two-dimensional electron gas in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs quantum wells. These lines were assigned to Landau-level transitions with an emission of coupled magnetoplasmon–LO-phonon modes. The couplings were found to increase strongly near the resonances between the energies of the LO phonon and multiples of the cyclotron energies.