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Tunable metal-insulator transition in double-layer graphene heterostructures

Cheianov interpreted the insulating behaviour observed in graphene-hBN-graphene sandwiches with one layer kept at the neutrality point while the other was heavily doped - in contrast to resistivity ~h/e^2 found in individual graphene flakes at zero density. Usually, electron-hole puddles due to substrate charges hide a true zero-density limit in graphene with short-range defects. Having modelled the screening of charges in the environment by a highly-doped second graphene flake (details in Supplementary Information) Cheianov demonstrated that puddles vanish, enabling one to observe the insulating behaviour at a zero density of electrons, due to their intervalley scattering.