Spatially Resolved Edge Currents and Guided-Wave Electronic States in Graphene
Fig. 1: ‘Fibre-optic’ modes and spatially resolved current imaging in a graphene Josephson junction*. [Reprinted by permission from Macmillan Publishers Ltd: Nature Physics ©2015]
Exploiting the light-like properties of carriers in graphene could allow extreme non-classical forms of electronic transport to be realized. In this vein, finding ways to confine and direct electronic waves through nanoscale streams and streamlets, unimpeded by the presence of other carriers, has remained a grand challenge.
In a Letter* to Nature Physics, Harvard Physics grad student Monica Allen and a group of colleagues from MIT, Israel, the Netherlands, and Japan, led by Prof. Amir Yacoby, proposed a novel way to address this challenge. Inspired by guiding of light in fibre optics, the authors demonstrated a route to engineer such a flow of electrons using a technique for mapping currents at submicron scales. They employed real-space imaging of current flow in graphene to provide direct evidence of the confinement of electron waves at the edges of a graphene crystal near charge neutrality. This was achieved by using superconducting interferometry in a graphene Josephson junction and reconstructing the spatial structure of conducting pathways using Fourier methods. The observed edge currents arise from coherent guided-wave states, confined to the edge by band bending and transmitted as plane waves. As an electronic analogue of photon guiding in optical fibres, the observed states afford non-classical means for information transduction and processing at the nanoscale.
*See M.T. Allen, O. Shtanko, I.C. Fulga, A.R. Akhmerov, K. Watanabe, T. Taniguchi, P. Jarillo-Herrero, L.S. Levitov & A. Yacoby, "Spatially resolved edge currents and guided-wave electronic states in graphene," Nature Physics (09 November 2015) doi:10.1038/nphys3534.