Term spectrum of magnetoexcitons in quasi-two-dimensional systems

We present highly resolved photoluminescence excitation spectra of undoped GaAs/${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As quantum wells in the presence of magnetic and electric fields. The high quality of our ${\mathit{p}}^{+}$-i-${\mathit{n}}^{+}$ sample, and the excitation with circularly polarized light, allow us, for the first time, to fully resolve the fine structure in the spectra. By comparison with calculations, which takes into account exciton mixing and external fields, we identify the ground and excited states of excitons in quasi-two-dimensional systems and are able to disclose its internal structure to a hitherto unprecedented detail.