  We present both the experimental and theoretical investigation of a
non-trivial electron Landau levels shift in magnetic field in wide ~20 nm HgTe
quantum wells: Landau levels split under magnetic fields but become degenerate
again when magnetic field increases. We reproduced this behavior qualitatively
within an isotropic 6-band Kane model, then using semiclassical calculations we
showed this behavior is due to the mixing of the conduction band with total
spin 3/2 with the next well subband with spin 1/2 which reduces the average
vertical spin from 3/2 to around 1. This change of the average spin changes the
Berry phase explaining the evolution of Landau levels under magnetic field.
