Extended Data Fig. 2: Independence of top and bottom gates.

a, Schematic of experimental devices with reference electrode. b, Voltage measured in the reference electrode, V_t^ref (red data points), as a function of V_b for a fixed V_t (black data points). The horizontal dashed arrows in the bottom axis indicate that the bottom gate is swept from −1.4 V to and from 1.4 V repeatedly for a fixed value of V_t. Vertical dashed line next to the left y-axis indicates that V_t is stepped from −1.4 V to 1.4 V. Left y-axis (black), applied V_t. Right y-axis (red), measured V_t^ref. c, Voltage measured in the reference electrode, V_t^ref (red data points), as a function of V_t for a fixed V_b (black data points). The horizontal and vertical lines next to x- and y-axis indicate the sweeping and stepping of the gates. Left y-axis (black), applied V_b. Right y-axis (red), measured V_t^ref.