Figure 2. Gate voltage and magnetic field dependence of the normal state resistance.

(a) Gate voltage dependence of the normal state resistance. The maximum at V_g~−10 V, provides a first indication of ambipolar transport. The V_g dependence originates from the modulation of the conductivity of the surface close to the gate, and can be quantitatively described as δσ(V_g)=n_Dirac(V_g)eμ (n_Dirac(V_g) is given by equation (1) with μ=2500 cm² Vs⁻¹ (inset of panel (a): the yellow line corresponds to the calculated δσ(V_g)). (b) Full dependence of the resistance on V_g and magnetic field B (the measurements are performed by sweeping V_g at fixed B, for different values of B). As a function of B the resistance increases approximately linearly, exhibiting clear oscillations that are enhanced by deriving the data with respect to either V_g or B. (c) Oscillations in −d²R/dB² (V_g=−62 V), periodic in 1/B as it is typical for the SdH effect (for small oscillations superimposed on a slowly varying background −d²R/dB² has the same phase as the oscillations in the resistance itself). All data shown in this figure were measured at 4.2 K.