Berlin 2012 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 15: Graphene: Structure and Theory I

HL 15.6: Talk

Monday, March 26, 2012, 16:15–16:30, EW 201

Opening of a tunable energy gap in disordered graphene nanoribbons — •George Pal, Walter Apel, and Ludwig Schweitzer — Physikalisch-Technische Bundesanstalt (PTB), Bundesalee 100, 38116 Braunschweig, Germany

The absence of an energy gap in the electronic band structure is the most severe impediment for the use of graphene in electronic device applications where large on-off currents are indispensable. Recently, we have proposed a mechanism to open a spectral gap by applying structured external electric potentials to the edge regions of graphene zig-zag nanoribbons [1]. Specifically, we show that an antisymmetric potential that acts selectively on the ribbon boundaries shifts the energies of the edge states in opposite directions and thus an energy gap opens up. To check the robustness of the proposed gap-opening mechanism against disorder, which is certainly present in real samples, we study the effect of different kinds of imperfections on the spectral and the transport properties. These include uncorrelated random on-site potentials, chiral-symmetry preserving bond disorder and edge disorder which may be due to edge passivation by randomly attached atoms that saturate the carbon dangling bonds. We find that all types of disorder merely reduce the spectral gap. Bulk disorder influences only slightly the edge states responsible for the gap, and its closing is mainly due to increasing the strength of edge disorder. Still, the energy gap remains finite as long as W<2V, where W is a measure of the disorder strength and V is the applied potential. [1] W. Apel, G. Pal and L. Schweitzer, PRB 83, 125431 (2011)