In 1957, John Bardeen, Leon Cooper, and John Robert Schrieffer came up with the first theory of superconductivity to describe how some materials can conduct electricity with no electrical resistance. However, there are many superconductive materials that cannot be described using this theory. Understanding the mechanism of unconventional superconductivity could help scientists engineer materials with higher transition temperatures. Pablo Jarillo-Herrero and colleagues now show that when two graphene sheets are twisted by a certain angle they exhibit unconventional superconductivity, with features similar to high-temperature superconducting cuprates. This system can easily be tuned through both the twist angle and electric fields, so could provide a new two-dimensional platform for understanding the origin of high-temperature superconductivity. Elsewhere in this issue, the same team reports that twisting graphene sheets in this manner also creates an insulating state that appears to be driven by strong electronic interactions, consistent with a Mott-like insulator phase.
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