One sheet of graphene can be a superconductor and an inslulator at the same time

Graphene is one of the weirdest materials on Earth. Stronger than steel, highly conductive, one atom thick, transparent in single sheets – scientists are still exploring all of the curious properties of graphene. For example, while graphene normally is very conductive, it can be a good insulator as well. Scientists at ETH Zurich have started exploring these properties.

Back in 2018 scientists at the Massachusetts Institute of Technology demonstrated that by placing one flake of graphene on top of another one turned precisely by 1.06 degrees this material can be turned into an insulator. When a specific voltage is applied the same flakes become superconductors. This is a very curious property, which would be extremely useful in electronics, because the same component could be an insulator and a superconductor at will. Now scientists in Switzerland showed that two separate flakes are not needed for this effect.

Researchers have now shown that the same insulator/superconductor switching can be created by bending sheets of graphene in very precise ways. This means that parts of the same flake can be superconductors while others are insulators. This effect, called Josephson junction, was achieved by applying different voltages to different parts of the flake until it folded in a very special way. It is possible to create zones of superconductivity separated by a thin strip of insulator. The thinness of it is limited by a quantum tunneling effect, which is a big puzzle in chip manufacturing, but scientists believe that this invention could be immensely useful.

Josephson junction could have important applications in quantum technologies. For example, scientists are thinking about SQUIDs (“superconducting quantum interference devices”), where Josephson junctions would form a ring. Scientists are thinking about employing this technology to realize different kinds of quantum bits (qubits) in a single device. Although scientists are thinking about more creative applications as well – Klaus Ensslin, lead author of the study, said: “So far, however, that’s just speculation. With the electrodes, we can practically play the piano on the graphene”.

Graphene is a very weird material, even though it is literally just carbon atoms arranged in a honeycomb lattice. It is one atom thick, but it can be layered. It is quite expensive to grow, but little by little it is making its way into our electronics. Superconductivity and insulating properties could help making very small electronic components, even though it is just a beginning of this research.

Source: ETH Zurich