A stack of two tilted graphene monolayers

Superconductivity in twisted bilayer graphene

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When two graphene lattices are overlaid and tilted, they can interfere to create a moiré pattern with a long period. At a small angle of about 1.1º, it was recently showed that the twisted bilayer graphene stack becomes superconducting. At this “magic” angle, the energy dispersion of electrons becomes flat and the interaction parameter becomes large. By tuning the carrier density, the twisted bilayer graphene stack becomes a Mott insulator. These properties are similar to those of cuprates and other high-temperature superconductors. Graphene has two key advantages compared to these materials. First, the band structure of monolayer graphene is simple and well understood. Second, the Fermi energy can be tuned by simply adjusting the voltage applied to the gate electrode in order to characterize the whole phase diagram of electrons. Twisted bilayer graphene represents a promising platform for understanding the elusive properties of unconventional superconductivity. This project is carried out in close collaboration with the group of Dima Efetov at ICFO.

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