Magneto-optical evidence of many-body effects in a spin-polarized two-dimensional electron gas

Modulation-doped CdxMn1-xTe/CdyMg1-yTe quantum wells are studied at 1.7 K by magnetoabsorption experiments performed near the fundamental heavy-hole-electron (HH1-E-1) transition. In the investigated range of Mn content (x approximate to 0.02) and electron concentration [n(e)approximate to(2-3)X10(11)cm-(2]), the two-dimensional electron gas is fully spin-polarized at magnetic fields as low as H=1.5 T. The interband optical spectra exhibit unusual magnetic field dependence resulting from electron-hole interactions and phase-space-filling effects. An additional enhancement of the spin splitting of Landau levels found in this study is attributed to the electron-exchange interaction. A simplified theoretical model including the exchange energy and the electron-hole interaction provides a coherent quantitative description of the overall experimental features.