Dresden 2009 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 15: C/diamond I
HL 15.12: Talk
Tuesday, March 24, 2009, 12:30–12:45, POT 51
Bound states and magnetic field-induced valley splitting in gate-tunable graphene quantum dots — •Patrik Recher1,2, Johan Nilsson1, Guido Burkard3, and Björn Trauzettel2 — 1Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands — 2Institute for Theoretical Physics and Astrophysics, University of Würzburg, 97074 Würzburg, Germany — 3Department of Physics, University of Konstanz, 78457 Konstanz, Germany
The magnetic field dependence of energy levels in gapped single- and bilayer graphene quantum dots (QDs) defined by electrostatic gates is studied analytically in terms of the Dirac equation. Due to the absence of sharp edges in these types of QDs, the valley degree of freedom is a good quantum number. We show that its degeneracy is efficiently and controllably broken by a magnetic field applied perpendicular to the graphene plane. This opens up a feasible route to create well-defined and well controlled spin- and valley-qubits in graphene QDs. We also point out the similarities and differences in the spectrum between single- and bilayer graphene quantum dots. Striking in the case of bilayer graphene is the anomalous bulk Landau level (LL) that crosses the gap which results in crossings of QD states with this bulk LL at large magnetic fields in stark contrast to the single-layer case where this LL is absent. We discuss the applicability of such QDs to control and measure the valley isospin and their potential use for hosting and controlling spin qubits.