Gate-defined Josephson junctions in magic-angle twisted bilayer graphene

In situ electrostatic control of two-dimensional superconductivity¹ is commonly limited due to large charge carrier densities, and gate-defined Josephson junctions are therefore rare^2,3. Magic-angle twisted bilayer graphene (MATBG)^4-8 has recently emerged as a versatile platform that combines metallic, superconducting, magnetic and insulating phases in a single crystal^9-14. Although MATBG appears to be an ideal two-dimensional platform for gate-tunable superconductivity^9,11,13, progress towards practical implementations has been hindered by the need for well-defined gated regions. Here we use multilayer gate technology to create a device based on two distinct phases in adjustable regions of MATBG. We electrostatically define the superconducting and insulating regions of a Josephson junction and observe tunable d.c. and a.c. Josephson effects^15,16. The ability to tune the superconducting state within a single material circumvents interface and fabrication challenges, which are common in multimaterial nanostructures. This work is an initial step towards devices where gate-defined correlated states are connected in single-crystal nanostructures. We envision applications in superconducting electronics^17,18 and quantum information technology^19,20.