Fig. 2: dI/dV_b(V_b, V_g) maps at an AA region.

a Shows the \({dI}/d{V}_{b}\)(\({V}_{b},{V}_{g}\)) maps at an AA region. At high gate voltages, the flat bands appear as two bright lines below the \({E}_{F}\) at \({V}_{b}=0 \;{{\rm{mV}}}\), indicating that they are fully filled. As the gate voltage is reduced the \({E}_{F}\) intersects the flat bands and they begin to empty. Since the density of states in the flat bands is very high the bands, seen as two horizontal bright lines, look pinned to \({E}_{F}\) as they slowly empty. Note that the lowest applied gate voltage of 23.3 V is not enough to fully empty the bands. In addition to these expected spectroscopic features, a series of oblique lines can be seen in a narrow gate range of 50–68 V. When these lines intersect the \({E}_{F}\), a series of faint coulomb diamonds are seen. These additional spectroscopic features indicate the presence of a quantum dot in the system. b is a zoomed-in view of the region marked by the white rectangle in a. c Some selected \({dI}/d{V}_{b}\) spectra from the gate dependence map which show the confinement peaks in the spectra only when the Fermi level is near the band edge. The evolution of the individual confinement peaks with gate voltage which appears as the oblique lines in a can also be seen.