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Give double-layer graphene a twist and it superconducts

A ‘magic angle’ lets electrons flow freely

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4:10pm, March 8, 2018
graphene

DOUBLE UP  A device made of two layers of graphene (illustrated) can conduct electricity without resistance when one layer is rotated relative to the other.

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LOS ANGELES — Give a graphene layer cake a twist and it superconducts — electrons flow freely through it without resistance. Made up of two layers of graphene, a form of carbon arranged in single-atom-thick sheets, the structure’s weird behavior suggests it may provide a fruitful playground for testing how certain unusual types of superconductors work, physicist Pablo Jarillo-Herrero of MIT reported March 7 at a meeting of the American Physical Society.

The discovery, also detailed in two papers published online in Nature on March 5, could aid the search for a superconductor that functions at room temperature, instead of the chilly conditions required by all known superconductors. If found, such a substance could replace standard conductors in various electronics, promising massive energy savings.

Layered graphene’s superconductivity occurs when the second layer of graphene is twisted relative to the first, at a “magic angle” of about 1.1 degrees, and when cooled below 1.7 kelvins (about –271° Celsius). Surprisingly, Jarillo-Herrero and colleagues report, the same material can also be nudged into becoming an insulator — in which electrons are stuck in place — by using an electric field to remove electrons from the material. That close relationship with an insulator is a characteristic shared by certain types of high-temperature superconductors, which function at significantly warmer temperatures than other superconductors, although they still require cooling.

The discovery of a material with behavior parallel to that of certain high-temperature superconductors could help explain the still-murky physics behind them (SN: 1/20/18, p. 11).  “We’re a little bit stuck. We have studied these materials to death,” Jarillo-Herrero said during a news conference on March 6. Twisted graphene might help scientists make progress on the topic.

Citations

P. Jarillo-Herrero. Topology, correlations, and superconductivity in 2D. American Physical Society March Meeting, Los Angeles, March 7, 2018.

Y. Cao et al. Unconventional superconductivity in magic-angle graphene superlattices. Nature. Published online March 5, 2018. doi:10.1038/nature26160.

Y. Cao et al. Correlated insulator behaviour at half-filling in magic-angle graphene superlattices. Published online March 5, 2018. doi:10.1038/nature26154.

Further Reading

E. Conover. Some high-temperature superconductors might not be so odd after all. Science News. Vol. 193, January 20, 2018, p. 11.

A. Grant. Graphene shows signs of superconductivity. Science News. Vol. 188, October 3, 2015, p. 7.

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