Elementary excitations in modulation-doped Cd(Mn)Te quantum wells

We report on the observation of dispersive elementary excitations of two-dimensional electron gases in modulation-doped CdTe and ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ quantum wells. From the plasmon dispersion, we deduce electron densities in good agreement with the ones deduced from independent experiments, provided that a finite lifetime of the electron-hole pairs is taken into account within a modified random phase approximation model. We also find in the same samples uncorrelated electron-hole excitations at energies significantly lower than expected from the electron density. We discuss the possible implications of these findings in terms of electron localization.