Quantum hall effect in a system of gapless Dirac fermions in HgTe quantum wells

The specific features of the quantum Hall effect (QHE) in a system of gapless Dirac fermions in HgTe quantum wells have been studied. It has been established that the behavior of the QHE is asymmetric with respect to the Dirac point: at the lowest temperature ($0.2$ K), quantization of hole fermions occurs in weak magnetic fields down to $0.15$ T, whereas quantization of the electron part of the Dirac cone occurs only in fields of about $0.5$ T. Such an asymmetry is caused by the effect of sideband maxima in the valence band forming the heavy-hole valleys, which play the role of a reservoir and screen out the fluctuation potential. The analysis of the behavior of the dissipative component of the conductivity near the Dirac point has led to a conclusion on the existence of the zeroth Landau level at this point.