Excitons in motion in II-VI semiconductors

We have shown recently that the magnetic properties of excitions change significantly as the excitions acquire kinetic energy. In particular, the excition magnetic moments are enhanced considerably, whilst the diamagnetism decreases. The behaviour can be investigated through spectrascopic studies of excitions confined in quantum wells of large width (greater than five times the excition Bohr radius) and these motion-induced changes in the magnetic properties have now been observed for CdTe, Znse, ZnTe and GaAs. The present paper summarises these phenomena. with particular focus on CdTe and ZnSe, and shows that the changes can be accounted or by motion induced mixing between the excition ground and higher lying states. The mixing is caused by the gamma term in the Luttinger Hamiltonian which describes the dispersion curves for the valence hand and, as a result the form of the excition wavefunction becomes motion dependent. For both materials, excellent agreement is obtained between experiment and the results predicted by this mechanism.