We study the transport properties of HgTe-based quantum wells containing simultaneously electrons and holes in a magnetic field $B$. At the charge neutrality point (CNP) with nearly equal electron and hole densities, the resistance is found to increase very strongly with $B$ while the Hall resistivity turns to zero. This behavior results in a wide plateau in the Hall conductivity ${\sigma }_{xy}\approx 0$ and in a minimum of diagonal conductivity ${\sigma }_{xx}$ at $\nu ={\nu }_p-{\nu }_n=0$, where ${\nu }_n$ and ${\nu }_p$ are the electron and hole Landau level filling factors. We suggest that the transport at the CNP point is determined by electron-hole “snake states” propagating along the $\nu =0$ lines. Our observations are qualitatively similar to the quantum Hall effect in graphene as well as to the transport in a random magnetic field with a zero mean value.

• Received 3 September 2009

DOI:https://doi.org/10.1103/PhysRevLett.104.166401