Two-dimensional charged magneto-excitons: magnetic translations and localization

For composite complexes - quasi-two-dimensional (2D) charged magneto-excitons X- - we propose a new exact classification of states, which is based on magnetic translations. We consider implications of this symmetry for magneto-optical transitions. It is shown, in particular, that in a translationally invariant system with a simple valence band, the ground triplet X-t(-) state is dark in interband transitions at finite magnetic fields B. This exact result calls for the re-interpretation of several previous theoretical studies. We consider the symmetry-breaking effects of spatial lateral confinement on internal transitions of charged complexes. (C) 2000 Elsevier Science B.V. All rights reserved.