Proximity induced Superconductivity in Epitaxial Graphene*

The intimate electrical contact of a superconductor with a normal metal leads to an exchange of carriers through their boundary. Cooper pairs leak into the normal metal via Andreev reflection and enable the normal metal to acquire superconducting-like properties. The electron-hole conversion process in graphene is prominent due to relativistic quantum mechanics governing low energy chiral carriers in a multi-valley system. In the present experiment, we reveal spatial measurements of the proximity effect in graphene from a graphene-superconductor interface. Superconducting aluminum films were grown on epitaxial graphene on SiC. The aluminum films were discontinuous with networks of trenches in the film morphology reaching down to the substrate to exposed graphene terraces. Scanning tunneling spectra measured on the graphene terraces show a clear decay of the superconducting gap width with increasing separation from the graphene-aluminum edges. The decay length for the superconducting energy gap extends beyond 400 nm. Subtle deviations in the exponentially decaying energy gap were also observed on a much smaller length scale of tens of nanometers.