Dresden 2014 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 42: Transport: Graphene (organized by TT)

TT 42.2: Talk

Tuesday, April 1, 2014, 10:00–10:15, WIL C107

Ab-initio simulations of local current flows in functionalized graphene flakes and ribbons — •Michael Walz, Alexei Bagrets, and Ferdinand Evers — Institute of Nanotechnology (INT) and Institut für Theorie der Kondensierten Materie (TKM), Karlsruhe Institut of Technologie (KIT), D-76131 Karlsruhe, Germany

Using our DFT-based transport framework AITRANSS [1,2], we calculate the transmission and the local current density in graphene flakes functionalized by adsorbed atoms, such as nitrogen or hydrogen.

We find that even a single nitrogen atom can almost completely suppress the conductance of a (gated) graphene armchair nano-ribbon. In this situation local ring currents emerge that result in local (orbital) magnetic moments.

As one expects, very wide ribbons (flakes, W≫ L) exhibit the bulk conductance G=2e²/hW/π L in the absence of adsorbants. With 20% hydrogen absorbants, we observe very complicated patterns of streamlines with many eddies and a broad distribution of local magnetic fields, B(r), that are induced by the dc-current flow. We plan to study the statistics of the conductance and B(r) of such large flakes and its dependency on the impurity concentration. Performing such calculations starting from first principles is challenging because of high computational costs. On this account, we parallelized our transport module AITRANSS using standard MPI and OpenMP techniques, also including Scalapack to treat systems up to 10.000 carbon atoms.

[1] A. Arnold et al., J. Chem. Phys. 126, 174101 (2007).

[2] J. Wilhelm, MW, et al., Phys. Chem. Chem. Phys. 15, 6684 (2013).