Extended Data Fig. 1: dI/dV curves on an AA site.
From: Cascade of electronic transitions in magic-angle twisted bilayer graphene
a, Optical micrograph of the MATBG/h-BN device from which data in main text Fig. 1 were acquired (device A). The white dashed line encloses the MATBG area. b, STM topographic image of 1.06° MATBG (Vb = −500 mV, I = 10 pA). c, dI/dV spectra acquired at the centre of an AA site, where both flat bands are completely filled (red), the valence flat band is filled but the conduction flat band is empty (purple), and both flat bands are completely empty (blue). These data were acquired on the same AA site as that shown in main text Fig. 1c. Sequential curves are vertically offset by 20 nS for clarity. d, Same as c but for more gate voltages (Vg = 50 V to −50 V). Sequential curves are vertically offset by 2.5 nS for clarity. A feature due to inelastic tunnelling is sometimes seen at Vb = ±60 mV but has no influence on observations closer to EF than36 ±60 mV. The dI/dV values for spectra with negative ν appear to be generically larger than for positive ν. This asymmetry is caused in part by the constant-current feedback condition in STS measurements. As ν decreases, the flat bands are emptied and contribute less to the tunnelling current at the set point; the tip moves closer to the sample to compensate for the loss in current, amplifying the value of dI/dV as ν decreases. We cannot however rule out the possibility that intrinsic electron–hole asymmetry also plays a role in the difference in dI/dV between positive and negative ν. e, −dEH/dVg as a function of gate voltage (rolling average over a ΔVg = 0.65 V window) obtained by extracting the energy EH of the peak in dI/dV for the cascade features shown in main text Fig. 1. Upward pointing triangles identify discontinuous transitions between each cascade feature in the conduction flat band (red), around charge neutrality (purple), and in the valence flat band (blue). f, dI/dV(Vb = 0 V, Vg) on the AA site. Equally spaced shaded bars are drawn over dips in the zero-bias conductance, which allow us to identify each integer filling ν of the flat bands. Zero-bias conductance peaks are marked by downward pointing triangles, which can be attributed to each of the discontinuities in a.
