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When two graphene sheets are stacked so that there is a specific angle between them, fascinating properties reminiscent of high-temperature superconductors emerge. Spectroscopy now provides insights into this behaviour.
Rotating two overlapping mesh grids relative to each other produces interference patterns called moiré fringes. In the past few years, scientists have started to engineer moiré fringes at the atomic scale by twisting single-atom-thick layers of suitable materials, such as graphene (a 2D honeycomb lattice of carbon atoms). In 2018, it was shown that, as the twist angle between two graphene sheets is tuned to about 1°, the physical properties of the system change dramatically1,2 to resemble those of high-temperature superconductors. To explore the microscopic physics of these surprising observations, four teams — Kerelsky et al.3, Xie et al.4 and Jiang et al.5 in Nature, and Choi et al.6 in a paper on the arXiv preprint server — have carried out spectroscopic measurements on twisted bilayer graphene.