Engineering correlated insulators in bilayer graphene with a remote Coulomb superlattice

Abstract Electron superlattices provide a powerful way to engineer novel correlated and topological quantum phenomena. Originally lithographic-patterned gate arrays were designed to create periodic superlattices in two-dimensional electron gases (2DEGs), where the superlattice potential can be continuously varied electrically. Fabricating superlattices at the nanometer scale with high precision, however, is challenging lithographically. Recently, moiré patterns in 2D materials have been found to offer near-perfect nanometer-scale electronic superlattices, which led to discoveries of exciting quantum phenomena in a variety of moiré heterostructures. However, the requirement of the moiré pattern poses a stringent limit on the material selection, and the moiré potential is not tunable for a given moiré heterostructure. To better engineer novel quantum phases, it will be desirable to create superlattices that combine the advantages of these two methods. Here we achieve this goal by engineering tunable correlated states in bilayer graphene with a remote Coulomb superlattice. The Coulomb superlattice is realized by localized electrons in a twisted bilayer WS2 that are 3 nm above the bilayer graphene. The period of the Coulomb superlattice is determined by the moiré period of the twisted bilayer WS2, and the strength of the superlattice potential is controlled by the number of localized electrons at the twisted bilayer WS2 moiré lattice site. We demonstrate that the 2DEG in encapsulated bilayer graphene is described by the Fermi liquid when the remote Coulomb superlattice is turned off. Electron correlation increases dramatically when the remote Coulomb superlattice is turned on, resulting in a series of correlated insulating states at both integer and fractional filling factors. This remote Coulomb superlattice can be applied to any 2D materials hosting a 2DEG. It opens a new route for in-situ control of correlated quantum phenomena in a wide variety of 2D systems.