Abstract
Wurtzite GaN on (0001) sapphire is studied by means of reflectance and magnetocircular dichroism up to 5.5 T at 2 K. This very powerful technique allows us to determine the Zeeman splittings to be about 0.05 meV/T for the X-A and X-C excitons and almost zero for the X-B exciton. Reflectance and dichroism are interpreted with a model of Gaussian dispersion of the excitonic energies and are in excellent agreement with previously proposed band-edge models.