Figure 3: THz QHE of the surface states.
From: Observation of the universal magnetoelectric effect in a 3D topological insulator
(a) The real part of the THz Hall conductivity σxy of two surfaces in units of 2e2/h, obtained at 
(symbols). The vertical solid lines indicate the positions of the Hall plateaus, estimated from the maxima in ∂σxy/∂B. Theoretical calculations represented by the thin line are performed as explained in the text. The inset presents the same experimental and theoretical curves in the whole magnetic field range, including the surface carrier CR at 0.4 T. (b) The plateau number as a function of the inverse magnetic field for different gate voltages. The lines are linear fits to N=hna/eB+1/2, where na corresponds to the carrier density on a single surface.
