Optimizing Dirac fermions quasi-confinement by potential smoothness engineering

Brun-Barrière, Boris [UCL - IMCN/NAPS & MODL, Université catholique de Louvain (UCLouvain), B-1348 Louvain-la-Neuve, Belgium] Moreau, Nicolas [UCL] Somanchi, S [JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, GERMANY] Nguyen, Viet-Hung [UCL] Mreńca-Kolasińska, A [AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Kraków, Poland] Watanabe, K [National Institute for Materials Science, Namiki, Tsukuba, Japan] Taniguchi, T [National Institute for Materials Science, Namiki, Tsukuba, Japan] Charlier, Jean-Christophe [UCL IMCN/NAPS & MODL, Université catholique de Louvain (UCLouvain), B-1348 Louvain-la-Neuve, Belgium] Stampfer, C [JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, GERMANY] Hackens, Benoît [UCL - IMCN/NAPS & MODL, Université catholique de Louvain (UCLouvain), B-1348 Louvain-la-Neuve, Belgium] et al.[show all]

With the advent of high mobility encapsulated graphene devices, new electronic components ruled by Dirac fermions optics have been envisioned and realized. The main building blocks of electronoptics devices are gate-defined p–n junctions, which guide, transmit and refract graphene charge carriers, just like prisms and lenses in optics. The reflection and transmission are governed by the p–n junction smoothness, a parameter difficult to tune in conventional devices. Here we create p–n junctions in graphene, using the polarized tip of a scanning gate microscope, yielding Fabry–Pérot interference fringes in the device resistance. We control the p–n junctions smoothness using the tipto-graphene distance, and show increased interference contrast using smoother potential barriers. Extensive tight-binding simulations reveal that smooth potential barriers induce a pronounced quasi-confinement of Dirac fermions below the tip, yielding enhanced interference contrast. On the opposite, sharp barriers are excellent Dirac fermions transmitters and lead to poorly contrasted interferences. Our work emphasizes the importance of junction smoothness for relativistic electron optics devices engineering.