The Ensslin team of the Swiss Federal Institute of Technology Zurich (ETH) used graphene to create the first superconducting quantum interference device to demonstrate the interference of superconducting quasiparticles. This greatly expands the range of uses for carbon graphene.
Related papers have been published in Nature Nanotechnology, DOI: 10.1038/s41565-022-01222-0. This research achievement is expected to promote the development of quantum technology and also open up new possibilities for superconductivity research.
In 2004, Konstantin Novoselov and Andre Geim created the first two-dimensional crystal composed of only one layer of carbon atoms. This material, named graphene, has attracted widespread attention and has been vigorously developed since then. Graphene is a new type of nanomaterial with the thinnest, highest strength, and best electrical and thermal conductivity. With the deepening of the research, more features of it have surfaced one by one.
Now, for the first time, ETH researchers have fabricated superconducting elements, known as SQUIDs (Superconducting Quantum Interference Devices), from double-layer twisted graphene to demonstrate the interference of superconducting quasiparticles. In quantum technology, these sensitive sensors are used as quantum bits (qubits). These basic elements can be used to perform quantum operations and build more complex circuits.
According to the official press release, this achievement first builds on research work by the team of Klaus Ensslin and Thomas Ihn at the ETH Solid State Physics Laboratory. IT House understands that they have demonstrated about a year ago that twisted bilayer graphene can be used to make Josephson junctions, the basic building blocks of superconducting devices.
However, the researchers were not satisfied with their breakthrough, because these graphene SQUIDs do not have many advantages over traditional aluminum SQUIDs, and like traditional SQUIDs, they also have to be cooled to near absolute zero ( 2 degrees above absolute zero).
According to Ensling, they have significantly expanded the range of applications: Five years ago, we were able to show that graphene could be used to make single-electron transistors. Now we've added superconductivity to it.
Depending on the applied voltage, graphene can change between insulating, conducting, and superconducting states. Furthermore, this result now shows that we can combine semiconductor transistors and superconductors in a single material to make new SQUIDs.
Enslin said, in quantum technology, SQUIDs can hold qubits and can therefore be used as components to perform quantum operations. Transistors are typically made of silicon and SQUIDs are made of aluminum, and different materials require different processing techniques, but now they can all be made from graphene.
According to Ensslin, their future research will focus on using graphene on the same crystal to combine the advantages of both quantum systems.
There are different superconducting phases within graphene, but there is no theoretical model to explain them yet. The latest results will also open up new possibilities for superconductivity research, and with these components, perhaps a better understanding of how superconductivity in graphene arises.
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