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 Cd0.98Mn0.02Te/Cd0.89Mg0.11Te single quantum well. The well width was 100Å and the concentration of two-dimensional electrons in the well was 3×1011cm−2. At magnetic fields lower than 7T and higher than 13T we observed a single electron cyclotron resonance (CR) line. Between 7 and 13T another absorption line appears in the spectra. These two lines exhibit an anti-crossing behavior with an energy gap of 2.5cm−1 at 8T. 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.