Figure 1: TLG heterojunction device schematic and electronic transport measurements.
(a) Schematic device representation. A narrow top gate is fabricated on a hBN-encapsulated Bernal-stacked TLG flake. A global, highly doped Si bottom gate controls electron density and the electrical displacement throughout the entire flake, whereas the top gate affects only the LGR. Interfaces between regions of different carrier type can be induced electrostatically at the LGR boundaries by appropriate choice of the top- and bottom-gate voltages. (b) AFM of the measured device. The black dashed lines indicate the TLG edges. Scale bar 4 μm. (c) Two terminal resistance data, R, acquired at temperature 300 mK and zero magnetic field. The resistance of the leads has been subtracted by removing a constant resistance corresponding to a uniform channel: ΔRLGR(VBG,VTG)=R(VBG,VTG)−R(VBG,0.37 V), where VBG is back-gate voltage and VTG is the top-gate voltage. Large amplitude oscillations are visible when the LGR is negatively doped (see arrows). The oscillations decay rapidly for large absolute density in the GLs. (d) Numerical derivative of the two terminal resistance, ∂R/∂VTG, at zero magnetic field. In addition to the giant oscillations, other resonances with smaller amplitude are visible throughout the bipolar regions, II and IV. (e) Numerical derivative of the two terminal resistance at magnetic field 200 mT. Although the small oscillations persist, the giant oscillations are completely suppressed by the classical confinement effect discussed in the main text.
