Spin-orbit and exchange interaction in surface quantum wells on gapless   semimagnetic semiconductor HgMnTe
  The first study of two-dimensional electron gas in surface layers on HgMnTe with inverted bands is carried out experimentally and theoretically. It is shown that the structure of investigated capacitance magnetooscillations in HgMnTe MOS structures is fully similar to the one in the non-magnetic narrow-gap semiconductor HgCdTe and the sole effect due to exchange interaction is the temperature shift of beat nodes. The information about exchange effects is obtained only due to our modeling of oscillations, because any pronounced changes in the position of oscillations are not observed and the separate spin components are not resolved. The Landau levels are calculated in the framework of concept we developed previously for the description of subband dispersions in zero magnetic field B=0. The new parameters (like those of $T/\sqrt{eB}$) arise in the theory of magnetooscillations in the semiconductors with quasirelativistic spectrum in contrast to the case of parabolic bands. The modeling shows that the spin-orbit splitting far exceeds a contribution due to exchange interaction. The calculated amplitudes of ``partial'' oscillations for different spin branches of spectrum are essentially different in accordance with the observed difference in the intensity of corresponding lines in Fourier spectra. The comparison between experiment and theory for different temperatures and parameters of exchange interaction is reported. The dominant mechanisms of the scattering responsible for the broadening of Landau levels are discussed. 
V.F. Radantsev, A.M. Yafyasov, V.B. Bogevolnov and I.M. Ivankiv