Dresden 2011 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 8: TR: Graphene 2 (jointly with MA, HL, and DY)

TT 8.9: Talk

Monday, March 14, 2011, 16:15–16:30, HSZ 304

Transport through a quantum-spin-Hall-insulator/normal junction in graphene ribbons — •Georgo Metalidis¹ and Elsa Prada² — ¹Institut für Theoretische Festkörperphysik and DFG-Center for Functional Nanostructures, Karlsruher Institut für Technologie, D-76128 Karlsruhe, Germany — ²Instituto de Ciencia de Materiales de Madrid (CSIC), Cantoblanco, 28049 Madrid, Spain

We have investigated a junction between a quantum-spin-Hall insulator and a metallic contact obtained by selectively doping a single graphene ribbon. In the absence of disorder, the transmission of the topological edge states through the junction is perfect due to the orthogonality of left- and right-movers. This is proven analytically by deriving exact wavefunctions for the topological edge states in armchair and zigzag ribbons. The wavefunction character depends fundamentally on the ribbon termination: the edge state width is only dependent on the spin-orbit coupling strength for armchair ribbons, whereas it is only weakly dependent of this parameter for zigzag edge states where the width becomes energy dependent instead. These observations are confirmed in numerical plots of the current density in the sample. When disorder is present, the orthogonality between left- and right-movers is destroyed and backscattering sets in. Nevertheless, the perfect transmission can be restored by increasing the ribbon width.