Graphene Makes Current Flow One Way express
A switch that knows which way to let current flow. That's how a Josephson diode works — a superconducting bridge where current goes willingly in one direction but meets resistance in the other. In the new study, such a bridge was made from graphene — a sheet of carbon just one atom thick.
The effect appeared when a weak magnetic field was applied, just a few millitesla, roughly the field of a fridge magnet. Rectification worked best near the dark fringes of the interference pattern, similar to the ripples from two stones dropped into water. There, efficiency exceeded 20%—a serious number for superconducting electronics.
The theoretical model showed that long-range scattering potentials are to blame. Simply put, inhomogeneities in the graphene itself. Even in an ultra-clean two-dimensional material, tiny defects remain, and they break the mirror symmetry of the junction. Without this breaking, the diode effect would not occur.
The authors suggest that the asymmetry could be controlled with external gates — special electrodes that modify the electric field in the junction. Then the diode would become tunable: turn a knob, and current flows the other way.
The Josephson junction is named after British physicist Brian Josephson, who predicted the effect in 1962 as a graduate student. He received the Nobel Prize just 11 years later.