  In the past two years, magic-angle twisted bilayer graphene has emerged as a
uniquely versatile experimental platform that combines metallic,
superconducting, magnetic and insulating phases in a single crystal. In
particular the ability to tune the superconducting state with a gate voltage
opened up intriguing prospects for novel device functionality. Here we present
the first demonstration of a device based on the interplay between two distinct
phases in adjustable regions of a single magic-angle twisted bilayer graphene
crystal. We electrostatically define the superconducting and insulating regions
of a Josephson junction and observe tunable DC and AC Josephson effects. We
show that superconductivity is induced in different electronic bands and
describe the junction behaviour in terms of these bands, taking in
consideration interface effects as well. Shapiro steps, a hallmark of the AC
Josephson effect and therefore the formation of a Josephson junction, are
observed. This work is an initial step towards devices where separate
gate-defined correlated states are connected in single-crystal nanostructures.
We envision applications in superconducting electronics and quantum information
technology as well as in studies exploring the nature of the superconducting
state in magic-angle twisted bilayer graphene.
