Resonant coupling of cyclotron and spin resonances in modulation-doped CdMnTe/CdMgTe quantum well structure

Abstract The far-infrared magneto-transmission measurements have been carried out on a modulation-doped Cd 0.98 Mn 0.02 Te/Cd 0.89 Mg 0.11 Te single quantum well. The well width was 100 A and the concentration of two-dimensional electrons in the well was 3×10 11  cm −2 . At magnetic fields lower than 7 T and higher than 13 T we observed a single electron cyclotron resonance (CR) line. Between 7 and 13 T another absorption line appears in the spectra. These two lines exhibit an anti-crossing behavior with an energy gap of 2.5 cm −1 at 8 T. We assign the new line to the spin-flip transitions between strongly spin-split (0, ↓) and (0, ↑) Landau levels. The spin-flip resonance (SFR) becomes observable in the experiment due to the resonant coupling between (0, ↑) and (1, ↓) Landau levels (LLs) as a result of which near the CR–SFR crossing the original magneto-dipole SFR becomes electric-dipole transition. We describe the data by a theoretical model proposed by Fal’ko taking into account the giant spin-splitting present in the CdMnTe quantum well. According to the model, the resonant coupling between the two LLs originates from the spin-orbit interaction. The observation illustrates that the spin-orbit interaction plays an important role in this 2D system.