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Nat Commun. 2017 Feb 17;8:14552. doi: 10.1038/ncomms14552.

Edge currents shunt the insulating bulk in gapped graphene.

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School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK.
National Graphene Institute, The University of Manchester, Booth St E, Manchester M13 9PL, UK.
School of Materials, The University of Manchester, Manchester M13 9PL, UK.
Department of Physics, University of Lancaster, Lancaster LA1 4YW, UK.
National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
Istituto Italiano di Tecnologia, Graphene Labs, Via Morego 30I-16163, Italy.


An energy gap can be opened in the spectrum of graphene reaching values as large as 0.2 eV in the case of bilayers. However, such gaps rarely lead to the highly insulating state expected at low temperatures. This long-standing puzzle is usually explained by charge inhomogeneity. Here we revisit the issue by investigating proximity-induced superconductivity in gapped graphene and comparing normal-state measurements in the Hall bar and Corbino geometries. We find that the supercurrent at the charge neutrality point in gapped graphene propagates along narrow channels near the edges. This observation is corroborated by using the edgeless Corbino geometry in which case resistivity at the neutrality point increases exponentially with increasing the gap, as expected for an ordinary semiconductor. In contrast, resistivity in the Hall bar geometry saturates to values of about a few resistance quanta. We attribute the metallic-like edge conductance to a nontrivial topology of gapped Dirac spectra.

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