Large-scale tight-binding simulations for graphene quantum dots and nanoribbons

Full text: Experimental progress in manufacturing and investigating nanoscale graphene dots on substrates as well as suspended nanoribbons have challenged theory to provide realistic descriptions of such large (≥106 atoms) yet finite systems. Unlike the ideal infinitely extended 2D graphene sheet whose low-energy spectrum close to the particle-hole crossover point can be described by a free Dirac fermion, nanoscale structures display a rich variety of lattice and confinement effects, bulk and surface disorder. We present an overview over our recent large-scale tight-binding simulations for quantum dots and nanoribbons [1-4]. We show that the transition of the diamagnetic dot spectrum in a strong magnetic field regime bears signatures of K-K' scattering due to disorder effects and differs dramatically from the simple Dirac picture. Coupling of the dot to the substrate can substantially alter and, in specific cases, simplify the dot wavefunction as the influence of edge disorder is suppressed. Transport through nanoribbons is found to be strongly influenced by bulk and edge disorder. Confinement quantization steps are strongly suppressed by symmetry-breaking defects. We observe a wide range of transport coefficients ranging from pronounced Anderson localization to nearly perfectly conducting channels. (authors) (*) work in collaboration with K. Ennsslin, F. Libisch, M. Morgenstern, S. Rotter, C. Stampfer. Supported by FWF (SFB-41 ViCom) References: 1. J. Guttinger, et al., Phys. Rev. Lett. 103, 046810 (2009) 2. F. Libisch, et al., Phys. Rev. 881, 245411 (2010) 3. F. Libisch, S. Rotter, J. Burgdorfer, Phys. Stat. Sol. B, (2011) 4. D. Subramaniam, et al., Phys. Rev. Lett. 108, 046801 (2012)