Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 86: Graphene VI

O 86.9: Talk

Friday, March 30, 2012, 12:30–12:45, MA 041

Anisotropic quantum Hall effect in graphene on stepped SiC(0001) surfaces — •Timo Schumann, Klaus-Jürgen Friedland, Myriano H. Oliveira Jr., J. Marcelo Lopes, and Henning Riechert — Paul-Drude-Institut für Festkörperelektronik, 10117 Berlin

The synthesis of epitaxial graphene on SiC by surface thermal decomposition is a promising route for future applications, since it produces high-quality and large-area layers directly on an insulating substrate. By this method, a regularly stepped graphene surface is formed with terrace widths in the order of µm and step heights of about 10 nm. Here we report on an anisotropic behavior in the magnetoresistance measured at high magnetic fields for narrow Hall bars patterned on stepped surfaces. The devices morphology and structural quality has been studied by atomic force microscopy and Raman spectroscopy. If the Hall bar is aligned parallel to the terraces, a quantum Hall effect with negative magnetoresistance is observed due to the condensation of the carriers in the Landau levels, away from the Fermi energy. In contrast, a positive magnetoresistance arises if the current crosses many steps (Hall bar perpendicular to the terraces). We tentatively explain this behavior by proposing a model, which is based on the opening of new conducting channels at both edges of the Hall bar in the surface region close to the steps. These additional channels enable the possibility of electron backscattering from one channel to another on the opposite side, since the spatial separation between the additional edge channels is reduced, resulting in a positive magnetoresistance.