Cyclotron resonance of conduction electrons in GaAs at very high magnetic fields

Cyclotron resonance of conduction electrons in GaAs was measured at a photon energy of 224 meV in magnetic fields up to 500 T produced by an electromagnetic flux compression. Cyclotron resonance and the corresponding transitions between donor states (magnetodonor transitions) were resolved at fields of about 190 T. The free-electron cyclotron resonance was successfully described by the five-level P⋅p model of band structure, which confirms the validity of the model up to 370 meV above the band edge. It was demonstrated that the spin g value goes through zero and changes sign as a function of magnetic field. Resonant and nonresonant polarons were included in the theory and it was found that the Fröhlich polaron coupling constant α=0.085 gives the best fit to the data. The experimental results of the magnetodonor transitions were analyzed and well accounted for by an effective two-level P⋅p model.