Figure 3

2D electron density maps in the atomic planes parallel to the surface of the sample at two extreme bias voltages: (a–c) under V_g = 3.2 V bias voltage at Z = 1.19, 1.36, 1.52 nm, respectively; (d–f) under V_g = −2.5 V bias voltage at Z = 1.19, 1.36, 1.52 nm, respectively. The Z positions for the 2D electron density maps are marked with arrows in Fig. 2b. The atoms contributing electron density to the different peaks are indicated. O_p designates CuO₂ plane oxygens; the peaks marked Cu/O_A tails are due to the electron density tails of the copper ion on one side and the apical oxygen ion on the other.