SPIN SPLIT CYCLOTRON-RESONANCE IN A 2-D ELECTRON-SYSTEM AT VERY HIGH MAGNETIC-FIELDS

Cyclotron resonance of the 2-Dimensional Electron System in GaAs/Ga0.6 6Al0.34As heterojunctions has been studied in very high (approximately 90 T) magnetic fields. The resonance is found to split into two compo nents due to the energy dependence of the electron g-factor. The exact magnitude of the splitting is slightly smaller than observed in bulk GaAs, but is found to be carrier concentration dependent. The intensit y of the two different transitions is also found to be carrier concent ration dependent, despite the fact that the electron g-factor of the L owest Landau state is close to zero. This behaviour is interpreted as due to collective electron effects similar to results observed at lowe r densities and lower temperatures in lower magnetic fields.