We have measured Raman scattering by LO phonons in GaAs in a magnetic field (≤12.8 T) at 10 K. The intensity displays Landau-level oscillations. This effect shows promise as a modulation technique for the investigation of interband magnetoabsorption. As an application we have studied the nonparabolicity of the ${\mathrm{\Gamma }}_1$ conduction band of GaAs for energies up to 0.4 eV above its bottom. Standard k⋅p expansions, including the ${\mathrm{\Gamma }}_1$ and ${\mathrm{\Gamma }}_{15}$ conduction and the ${\mathrm{\Gamma }}_{15}$ valence bands, cannot explain the observed dispersion. It can be explained by inclusion of interactions with higher bands.

• Received 27 May 1987

DOI:https://doi.org/10.1103/PhysRevLett.59.700