Magneto-optical studies have been conducted on two ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs superlattices to investigate excitonic transitions at the saddle points formed at ${\mathit{q}}_{\mathit{z}}$=π/d of the superlattice miniband structure. We report on a direct observation of both the E1(Π)-HH1(Π) saddle-point exciton and the indirect E1(Γ)-HH1(Π) excitonic resonance in both perpendicular and parallel magnetic fields, with both features showing perpendicular field-induced (Γ-Π) mixing in the separate carrier minibands. Theoretical calculations demonstrate highly field- and wave-vector-dependent valence-band g factors, which, because of the small valence-band widths, lead to the inversion of the ${\mathit{m}}_{\mathit{j}}$=+3/2 E-${\mathit{q}}_{\mathit{z}}$ dispersion curves at high perpendicular fields. The unusual behavior of the light-hole transitions indicates a large degree of in-plane mixing of the heavy- and light-hole states, which would appear to be closely linked to the observed wave-vector mixing and complex g factors.

• Received 21 August 1991

DOI:https://doi.org/10.1103/PhysRevB.45.4266