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Graphene, a single sheet of carbon atoms, has many extreme electrical and mechanical properties. Two years ago, researchers showed how two sheets laid on top of each other and twisted at just the right angle can become superconducting, so that the material loses its electrical resistivity. New work explains why this superconductivity happens in a surprisingly high temperature.

Researchers at Aalto University and the University of Jyv盲skyl盲 showed that graphene can be a superconductor at a much higher temperature than expected, due to a subtle quantum mechanics effect of graphene's electrons. The results were published in 萌妹社区ical Review B. The findings were highlighted in 萌妹社区ics viewpoint by the American 萌妹社区ical Society, and looks set to spark lively discussion in the physics community.

The discovery of the superconducting state in twisted bilayer graphene was selected as the 萌妹社区ics breakthrough of the year 2018 by the 萌妹社区ics World magazine, and it spurred an intense debate among physicist about the origin of superconductivity in graphene. Although superconductivity was found only at a few degrees above the absolute zero of temperature, uncovering its origin could help understanding high-temperature superconductors and allow us to produce superconductors that operate near room temperature. Such a discovery has been considered one of the "holy grails" of physics, as it would allow operating computers with radically smaller energy consumption than today.

The new work came from a collaboration between P盲ivi T枚rm盲's group at Aalto University and Tero Heikkil盲's group at the University of Jyv盲skyl盲. Both have studied the types of unusual superconductivity most likely found in graphene for several years.

"The geometric effect of the wave functions on superconductivity was discovered and studied in my group in several model systems. In this project it was exciting to see how these studies link to real materials," says the main author of the work, Aleksi Julku from Aalto University. "Besides showing the relevance of the geometric effect of the wave functions, our theory also predicts a number of observations that the experimentalists can check," explains Teemu Peltonen from the University of Jyv盲skyl盲.