Ballistic Transport in Graphene pnp Junctions Formed by Embedded Local Gates

Due to its gapless energy spectrum, one enables to tune the carrier type and density in graphene and realize pnp-type potential barriers in situ by using electrostatic gating. Such potential barriers provide opportunities to investigate novel phenomena such as Klein tunneling and quantum-Hall edge-state equilibration. In this study, we obtained high-quality graphene pnp junctions by embedding pre-patterned local gates in a substrate without dielectric-layer deposition or electron-beam exposure of the graphene sheet. We achieved ballistic and phase-coherent carrier transport in a graphene pnp device with a 130-nm-wide local gate, which is almost an order magnitude wider than reported previously[1]. In a high magnetic field, device with a 1-micro meter-wide local gate exhibited the $2e^{2}/h$ quantum-Hall plateau, indicating no backscattering in the local gate region. The conductance across our pnp junctions shows a gate-voltage dependence that is very distinctive from that of top-gated junctions, indicating a strong screening of the electric field by the embedded local gate. [1] A. F. Young and P. Kim, Nature Physics $\textbf{5}$, 222 (2009)