Reconfigurable edge-state engineering in graphene using LaAlO₃/SrTiO₃ nanostructures

The properties of graphene depend sensitively on doping with respect to the charge-neutrality point (CNP). Tuning the CNP usually requires electrical gating or chemical doping. Here, we describe a technique to reversibly control the CNP in graphene with nanoscale precision, utilizing LaAlO₃/SrTiO₃ (LAO/STO) heterostructures and conductive atomic force microscope (c-AFM) lithography. The local electron density and resulting conductivity of the LAO/STO interface can be patterned with a conductive AFM tip [Cen et al., Nat. Mater. 7, 298 (2008)] and placed within two nanometers of an active graphene device [Huang et al., APL Mater. 3, 062502 (2015)]. The proximal LAO/STO nanostructures shift the position of graphene CNP by ∼10¹² cm^-2 and are also gateable. Here, we use this effect to create reconfigurable edge states in graphene, which are probed using the quantum Hall effect. Quantized resistance plateaus at h/e² and h/3e² are observed in a split Hall device, demonstrating edge transport along the c-AFM written edge that depends on the polarity of both the magnetic field and direction of currents. This technique can be readily extended to other device geometries.