  Energy spectra both of the conduction and valence bands of the HgTe quantum
wells with a width close to the Dirac point were studied experimentally.
Simultaneous analysis of the Shubnikov-de Haas oscillations and Hall effect
over a wide range of electron and hole densities gives surprising result: the
top of the valence band is strongly split by spin-orbit interaction while the
splitting of the conduction band is absent, within experimental accuracy.
Astonishingly, but such a ratio of the splitting values is observed as for
structures with normal spectrum so for structures with inverted one. These
results do not consistent with the results of kP calculations, in which the
smooth electric filed across the quantum well is only reckoned in. It is shown
that taking into account the asymmetry of the quantum well interfaces within a
tight-binding method gives reasonable agreement with the experimental data.
