  Very high precision measurements of the electron Lande g-factor in GaAs are
presented using spin-quantum beat spectroscopy at low excitation densities and
temperatures ranging from 2.6 to 300 K. In colligation with available data for
the temperature dependent effective mass a temperature dependence of the
interband matrix element within a common five level kp-theory can model both
parameters consistently. A strong decrease of the interband matrix element with
increasing temperature consistently closes a long lasting gap between
experiment and theory and substantially improves the modeling of both
parameters.
