A first for a superconducting diode without an external magnetic field

Superconductors are the key to lossless current flow. However, the realization of superconducting diodes has only recently become an important subject of fundamental research. An international research team involving theoretical physicist Mathias Scheurer from the University of Innsbruck has now succeeded in achieving an important milestone: the realization of a superconducting diode effect without an external magnetic field, thus proving the hypothesis that superconductivity and magnetism coexist. They talk about it in Character Physics.

We talk about the superconducting diode effect when a material behaves like a superconductor in one direction of current flow and as a resistance in the other. Unlike a conventional diode, such a superconducting diode has completely zero resistance and therefore no loss in the forward direction. This could form the basis of future lossless quantum electronics. Physicists first succeeded in creating the diode effect approximately two years ago, but with some fundamental restrictions. “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 for Theoretical Physics at the University of Innsbruck. .

New experiments by experimental physicists at Brown University, described in the current issue of Character Physics, do not require an external magnetic field. In addition to the aforementioned application-related advantages, the experiments confirm a thesis previously theorized by Mathias Scheurer: namely that superconductivity and magnetism coexist in a system composed of three layers of graphene 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 also very strong. Additionally, the direction of the diode can be reversed by a very simple electric field. Together, this makes three-layer graphene such a promising platform for the superconducting diode effect,” says Mathias Scheurer, who was awarded an ERC Commencing Grant this year for his research on two-dimensional materials, in particular graphene.

Graphene, a promising material

The diode effect described in Nature Physics was also produced with graphene, a material made up of a single layer of carbon atoms arranged in a honeycomb. Stacking multiple layers of graphene leads to completely new properties, including the ability of three layers of graphene twisted against each other to conduct electrical current without loss. 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 three-layer 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. The theoretical basis for this has already been published in another high-ranking publication.

Magnetic FieldDiodeGrapheneInnsbruckMagnetismTheoretical PhysicsSuperconductivityUniversity

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