Harvard scientists open Trilayer Graphene Breakthrough opens the door to high-temperature superconductors

Interpretation of trilayer twisted layer graphene. Credits: Polina Shmatkova and Margarita Davydova

In 2018, the world of physics was set on fire with the discovery called an ultra-thin layer of carbon graphene, accumulates into a “magic angle” and this new double-layer structure becomes a superconductor, allowing electricity to pass without resistance or wasted energy. Now, literally twisted, Harvard scientists have expanded this superconducting system by adding and rotating a third layer, opening the door to continued advances in graphene-based superconductivity.

The work is explained in a new article Science and may one day contribute to superconductors that operate at higher or even closer ambient temperatures. These superconductors are considered to be the holy grail of condensed matter physics, as they would allow a tremendous technological revolution in many sectors, including electricity transportation, transportation, and quantum computing. Most superconductors today, including a double-layer graphene structure, operate only at ultra-cold temperatures.

“The superconductivity of twisted graphene provides physicists with an experimentally controlled and theoretically available model system to decode the secrets of high-temperature superconductivity so that they can play with the properties of the system,” said Andrew Zimmerman, one of the authors of the postdoctoral fellowship. Philip Kim working in the laboratory of Harvard physicist.

It is a grapheneatom-the thick layer of carbon atoms is 200 times stronger than steel, yet it is much more flexible and lighter than paper. It has almost always been known that it is a good conductor of heat and electric current, but it is very difficult to handle. Experiments to unlock the double-layer graphene puzzle have been ongoing WITH ONE Physicist Pablo Jarillo-Herrero and his team were at the forefront of the field of “twistronics” with their experiment in 2018, where they produced a superconductor of graphene by rotating it to a magic angle of 1.1 degrees.

Harvard scientists report that they have stacked three sheets of graphene and then rotated each of these magic angles to create a three-layer structure capable of achieving superconductivity, but one that performs more strongly and at higher temperatures than many double piles. graphene. The new and improved system is sensitive to externally applied electric field, allowing the level of superconductivity to be tuned, adjusting the strength of that field.

“It has allowed us to observe the superconductor in a new dimension and has given us important clues about the mechanism that drives superconductivity,” said Zeyu Hao, other lead author of the doctoral study. Undergraduate student in the School of Arts and Sciences who works in the Kim Group.

One of these mechanisms has the theorists very excited. The layer-by-layer system proved that its superconductivity is a strong interaction between electrons in the face of the weak. If true, this may help pave the way for high-temperature superconductivity, as well as possible applications in quantum computing.

“In most conventional superconductors, electrons move at high speed and intersect at intervals and interact with each other. In this case, we said that the effects of their interaction are weak, “said Eslam Khalaf, author of the study and a postdoctoral fellow who worked in the laboratory of Harvard physics professor Ashvin Vishwanath.” Although weak superconducting interactions are brittle and lose superconductivity when heated to some Kelvin. superconductors are much more resilient but much less understood. Realizing strong superconducting couplings can pave the way in a simple, tunable system like a trilayer that will eventually help develop a theoretical understanding of highly coupled superconductors to help achieve the goal of a high temperature, perhaps ambient temperature, superconductor. “

Researchers plan to continue to study the nature of this unusual superconductivity in further research.

“The more we understand, the better chance we have of increasing the transition temperatures of superconductors,” Kim said.

Reference: February 4, 2021, Science.

Funding: National Science Foundation, Department of Defense, Simons’ collaboration on ultra-quantum matter

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