(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.
Ultra-clean graphene
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.