  We study theoretically the magnetic field effect on a neutral, but
polarizable exciton confined in quantum-ring structures. For excitons with a
nonzero dipole moment, a novel magnetic interference effect occurs: The ground
state of an exciton confined in a finite-width quantum ring possesses a nonzero
angular momentum with increasing normal magnetic field. This effect is
accompanied by a suppression of the photoluminescence in well-defined
magnetic-field intervals. The magnetic interference effect is calculated for
type-II quantum dots and quantum rings.
