Researchers from Brown University, the University of New South Wales, Columbia University, University of Innsbruck, and the National Institute for Materials Science in Japan have carried out new experiments involving trilayer graphene, in which an external magnetic field is not required in order to achieve the 'superconducting diode effect' - a material that behaves like a superconductor in one direction of current flow and like a resistor in the other.
In contrast to a conventional diode, such a superconducting diode exhibits a completely vanishing resistance and thus no losses in the forward direction. This could form the basis for future lossless quantum electronics. Physicists have already succeeded in creating the diode effect, but with some fundamental limitations. "At that time, the effect was very weak and it was generated by an external magnetic field, which is very disadvantageous in potential technological applications," explains Mathias Scheurer from the Institute of Theoretical Physics at the University of Innsbruck. The new experiments confirmed a thesis previously theorized by Scheurer: Namely, that superconductivity and magnetism coexist in a system consisting of three graphene layers twisted against each other. The system thus virtually generates its own internal magnetic field, creating a diode effect.
"The diode effect observed by colleagues at Brown University was additionally very strong. Moreover, the diode direction can be reversed by a simple electric field. Together, this makes trilayer graphene such a promising platform for the superconducting diode effect," clarifies Mathias Scheurer, who received an ERC Starting Grant this year for his research on two-dimensional materials, among which is graphene.
The fact that a superconducting diode effect exists without an external magnetic field in this system has great implications for the study of the complex physical behavior of twisted trilayer graphene, as it demonstrates the coexistence of superconductivity and magnetism. This shows that the diode effect not only has technological relevance, but also has the potential to improve our understanding of fundamental processes in many-body physics.