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When rotated at a ‘magic angle’, graphene sheets can form an insulator or a superconductor

A large-scale interpretation of the moiré patterns formed when one graphene lattice is slightly rotated at a 'magic angle', with respect to a second graphene lattice. Credit: MIT

In November, we reported on moiré​ and how it may be able to push the boundaries of electronics. Now it may have.

Physicists at MIT and Harvard University claim they are able to tune graphene to behave as an insulator and a superconductor.

Previously experiments have led to synthesized graphene superconductors, but this latest development appears to demonstrate a way to make graphene superconduct independently.

The team claim they were able to show that superconductivity can be an intrinsic quality in the purely carbon-based material.

This was accomplished by creating a superlattice of two graphene sheets stacked together, not on top of each other but in a precise angle of 1.1°.

The physicists say that as a result, the overlaying, hexagonal honeycomb pattern is offset slightly, creating a precise moiré configuration that is predicted to induce strange, ‘strongly correlated interactions’ between the electrons in the graphene sheets.

The team, led by associate professor Pablo Jarillo-Herrero of MIT, found that when rotated at this ‘magic angle’, the two sheets of graphene exhibited non conducting behaviour, similar to Mott insulators.

When the researchers then applied voltage, adding small amounts of electrons to the graphene superlattice, they found that, at a certain level, the electrons broke out of the initial insulating state and flowed without resistance, as if through a superconductor.

“We can now use graphene as a new platform for investigating unconventional superconductivity,” Jarillo-Herrero explains. “One can also imagine making a superconducting transistor out of graphene, which you can switch on and off, from superconducting to insulating. That opens many possibilities for quantum devices.”

For more information about this research, click here and to read our report on moiré, click here.

Bethan Grylls

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