(July 29, 2015) Scientists at TU Delft and Leiden University have observed supercurrents in graphene that bounce back and forth between the edges of the graphene without scattering along the way. Supercurrents are electrical currents that flow even when there is no voltage applied. They can be induced in graphene by bringing it in contact with a superconducting material. The ability to create such ballistic superconductor-graphene hybrids makes it possible to study the unique properties of supercurrents carried by relativistic particles in an unexplored regime. These results have been published in Nature Nanotechnology.
The use of high-quality graphene is of vital importance for the performance of these devices. Being an atomically thin material, graphene is extremely sensitive to the ruggedness of its support structure and all dirt down to the atomic scale. In particular, during typical nanofabrication processes graphene is inevitably exposed to several polymers and chemicals, which easily stick to its surface making it dirty and thus degrading its electronic quality.
In order to circumvent this, the researchers first sandwich the graphene between two thin layers of boron nitride – an atomically flat insulator. This encasing effectively preserves the graphene in its pristine state by protecting it from the outside world. Finally, this stack is cut to the desired shape and the graphene is contacted from the side to the superconducting material.