Tunable fractional quantum Hall point contacts in graphene via local anodic oxidation of graphite gates

In an all-van der Waals heterostructure, the active layer, gate dielectrics, and gate electrodes are all assembled from two-dimensional crystals. Owing to the absence of dangling bonds within their two-dimensional bulk, these devices host ultraclean electron systems. Here, we describe methods for implementing nanoscale electrostatic control without contaminating critical interfaces. Using a resist-free local anodic oxidation process, we pattern sub-100 nm features in graphite gates which are then integrated into the heterostructure. Using a quantum point contact as a benchmark device, we demonstrate selective partitioning of both integer and fractional quantum Hall edge modes at high magnetic fields. Furthermore, we find evidence for fragile interaction-driven edge reconstruction effects, including the formation of a quantum dot at an electrostatic potential saddle point. Our results pave the way for precision nanoscale experiments on correlated states in these materials, including single anyon control in the fractional quantum Hall regime. 1 to interface (e.g. between the east and north gates), the confining potential Φ ext gives a confinement energy E V ≈ and 0 . 55 E C for three scenarios Fig. S5a-c respectively. We leave a more detailed study of the interplay of integer and fractional reconstruction in this QPC geometry to future work.