Interacting Landau and Stark quantizations in superlattices under high magnetic fields

Optical interband experiments in superlattices under simultaneous application of magnetic and electric fields are presented. For electric and magnetic fields parallel to the growth axis of the superlattice, Landau ladders associated to each Stark transition are observed. These Landau ladders are coupled and anticross as the ratio between magnetic and electric field is varied. For magnetic fields perpendicular to the electric field, on the other hand, the two fields are in direct competition to determine the nature of the exciton states and the localization of the wave functions. Increasing the magnetic field continuously transforms the exciton states from Stark-like to Landau-like. Comparison with a theoretical model for the calculation of exciton energies and absorption strengths gives very good agreement with experiment.