Fig. 4

a Hall resistivity for different carrier concentrations, controlled by the gate. b Dependence of the nonlocal resistance on the gate voltage and magnetic field for sample S2 (three-dimensional plot) and Hall resistance map (two-dimensional surface) showing regions of QHE for electrons (ν = 1), holes (ν = −1). c Calculated energy dispersion and d Landau level positions as a function of the magnetic field for sample S2