New twist in layered graphene could advance superconductivity

5 Feb 2021

Twisted trilayer graphene. Image: Polina Shmatkova and Margarita Davydova

Two separate research teams are working on triple-layered graphene structures that could open the door for high-temperature superconductors.

The potentials of so-called ‘wonder material’ graphene, have been talked about in the science community for a number of years. It is a one-atom-thick layer of carbon atoms that is 200 times stronger than steel, yet is extremely flexible and lighter than paper.

In 2018, scientists discovered that by creating a sandwich of two graphene layers, each just an atom thick, and twisting it at the ‘magic angle’ of 1.1 degrees, it shows superconductive properties.

Now, the group of researchers at MIT who made that initial discovery have expanded on the superconducting system by adding a third layer and rotating it, opening the door for new advancements in graphene-based superconductivity.

They reported observing superconductivity in a sandwich of three graphene sheets, with the middle layer twisted at a new angle of 1.56 degrees with respect to the outer layers.

In a paper published in Nature earlier this week, the team said this new trilayer configuration exhibits superconductivity that is more robust than its bilayer counterpart.

“We thought, why not, let’s give it a try and test this idea,” said Pablo Jarillo-Herrero of MIT. “Our structure is a nanosandwich.”

Another group of researchers from Harvard also expanded on the original bilayer, with a paper published in Science on Thursday (4 February).

Building on the work Jarillo-Herrero and his group pioneered in the emerging field of ‘twistronics’ in 2018, the Harvard team reported successfully stacking three sheets of graphene and then twisting each of them at the ‘magic angle’ of 1.1 degrees to produce a three-layered structure that is capable of robust superconductivity.

Potential for high-temperature superconductors

What is unique about these latest breakthroughs is that they open the door for high-temperature superconductors.

While most superconductors today only work at ultra-cold temperatures, including the double-layered graphene structure from 2018, both teams of scientists report that their trilayer graphene structures working at relatively high temperatures.

Andrew Zimmerman, a member of the Harvard team and co-lead author of the paper, said: “Superconductivity in twisted graphene provides physicists with an experimentally controllable and theoretically accessible model system where they can play with the system’s properties to decode the secrets of high-temperature superconductivity.”

Both research teams also said the trilayer structure is sensitive to an externally applied electric field that allows them to tune the level of superconductivity by adjusting the strength of that field.

The MIT researchers plan to fabricate twisted graphene structures with more than three layers to see whether such configurations can exhibit superconductivity at higher temperatures, even approaching room temperature.

“If we could make these structures as they are now, at industrial scale, we could make superconducting bits for quantum computation, or cryogenic superconductive electronics, photodetectors, etc. We haven’t figured out how to make billions of these at a time,” said Jarillo-Herrero.

Jenny Darmody is the editor of Silicon Republic