Excitons in dense two-dimensional electron-hole magnetoplasmas

We report clear excitonic effects in the optical spectra of neutral, dense magnetoplasmas in an ${\mathrm{In}}_{0.53}$ ${\mathrm{Ga}}_{0.47}$As/InP quantum well at low temperatures. The observed suppression of the density dependence of the uppermost occupied (${\mathit{j}}_{\mathit{e}}$=${\mathit{j}}_{\mathit{h}}$=N) Landau-level transition energies in the range of filling factors N<ν/2<N+1 is direct evidence that electrons and holes from the Nth Landau levels bind into magnetoexcitons. The effect disappears with increasing temperature. Good agreement between experimental results and theoretical calculations is obtained by including both the inter-Landau-level coupling and screening effects.