Dresden 2009 – scientific programme

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O: Fachverband Oberflächenphysik

O 15: Focused Session: Epitaxial Graphene II

O 15.2: Talk

Monday, March 23, 2009, 15:30–15:45, SCH 251

Effects of periodic potentials in graphene — •Ervand Kandelaki, Sam Shallcross, and Oleg Pankratov — Lehrstuhl für Theoretische Festkörperphysik, Staudtstr. 7-B2, 91058 Erlangen

For epitaxial graphene grown on the Si-face of SiC one expects a covalent bonding[1] and hence a significant impact of the substrate on the properties of graphene. Density-functional ab initio calculations[2] as well as experimental data[3] reveal the emergence of the long-periodic 6√3×6√3 superstructure in the first carbon layer which plays the role of a buffer layer and does not possess graphene’s characteristic spectrum. This superstructure generates a long-periodic perturbation then transmitted to a second “genuine graphene” layer. The large scale and complexity of the system invites the use of a continuum approximation to model the low energy excitation spectrum. The appropriate effective Hamiltonian is thus the Dirac-Weyl Hamiltonian with an additional periodic potential. We investigate the electronic spectrum of this effective Hamiltonian via the Korringa-Kohn-Rostocker method which is widely used for Schrödinger particles in a periodic potential. The main benefit of this method is the separation of the geometrical part, given by periodicity of the external potential, from the single-site scattering problem. The latter can be solved for any cylindrically symmetric potential. The impact upon the spectrum of various parameters such as potential periodicity, perturbation amplitude, and single-site scatterer type are discussed. [1] A. Mattausch and O. Pankratov, Phys. Rev. Lett. 99, 076802 (2007). [2] S. Kim et al., Phys. Rev. Lett. 100, 176802 (2008). [3] C. Riedl et al., Phys. Rev. B 76, 245406 (2007).