We have fabricated a Hall bar device on epitaxial graphene and measured a quantum Hall resistance quantization accuracy of three parts per billion at 300mK (Ref.1), reaching metrological accuracy. In the next step we have learned how to control the carrier concentration in graphene using a novel heterostructure of epitaxial graphene grown on silicon carbide combined with two polymers. By UV light exposure of this heterostructure we have changed the carrier concentration in graphene by a factor of 50 in a non-invasive, non-volatile, and reversible way. (Ref.2). The newly developed photochemical gating has already helped to improve the robustness of a graphene resistance standard, further improving the quantization accuracy by a factor of 30. (Refs.3,5) As a result of these refinements, it was possible to perform the first direct comparison of the integer quantum Hall effect (QHE) in epitaxial graphene with that in GaAs/AlGaAs heterostructures. No difference was found in the quantized resistance value within the relative standard uncertainty of the measurement of 8.6×10−11, this being the most stringent test of the universality of the Quantum Hall Effect in terms of material independence (Ref.4). It was shown that an excellent graphene device performance in these measurements is not simply the result of a larger device but finds its origin in a charge exchange mechanism between the SiC substrate and graphene, leading to an unusually strong pinning of the quantum Hall state in epitaxial graphene.
1. A. Tzalenchuk, S. Lara-Avila, A. Kalaboukhov, S. Paolillo, M. Syväjärvi, R. Yakimova, O. Kazakova, T. J. B. M. Janssen, V. Fal'ko, S. Kubatkin, Towards a quantum resistance standard based on epitaxial graphene, NATURE NANOTECHNOLOGY, 5, p.186, (2010).
2. S. Lara-Avila, K. Moth-Poulsen, R. Yakimova, T. Bjørnholm, V. Fal’ko, A. Tzalenchuk, S. Kubatkin, Non-volatile photochemical gating of an epitaxial graphene/polymer heterostructure, Adv.Mater.,23,878,(2011).
3. T. J. B. M. Janssen, A. Tzalenchuk, R. Yakimova, S. Kubatkin, S. Lara-Avila, S. Kopylov,V. I. Fal’ko, Anomalously strong pinning of the filling factor ν = 2 in epitaxial graphene, PHYSICAL REVIEW B 83, 233402, (2011).
4.T. J. B. M. Janssen, N.E. Fletcher, R. Goebel, J. M. Williams, A. Tzalenchuk, R. Yakimova, S. Kubatkin, S. Lara-Avila, V. I. Falko, Graphene, universality of the quantum Hall effect and redefinition of the SI system, New Journal of Physics 13, 093026, (2011).
5. T. J. B. M. Janssen, J. M. Williams, N. E. Fletcher, R. Goebel, A. Tzalenchuk, R. Yakimova, S. Lara-Avila, S. Kubatkin, V. I. Fal’ko, Precision comparison of the quantum Hall effect in graphene and gallium arsenide, Metrologia 49, 294, (2012).
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