Tunable quantum interferometer for correlated moir electrons

Magic-angle twisted bilayer graphene can host a variety of gate-tunable correlated states - including superconducting and correlated insulator states. Recently, junction-based superconducting moire devices have been introduced, enabling the study of the charge, spin and orbital nature of superconductivity, as well as the coherence of moire electrons in magic-angle twisted bilayer graphene. Complementary fundamental coherence effects-in particular, the Little-Parks effect in a superconducting ring and the Aharonov-Bohm effect in a normally conducting ring - have not yet been reported in moire devices. Here, we observe both phenomena in a single gate-defined ring device, where we can embed a superconducting or normally conducting ring in a correlated or band insulator. The Little-Parks effect is seen in the superconducting phase diagram as a function of density and magnetic field, confirming the effective charge of 2e. We also find that the coherence length of conducting moire electrons exceeds several microns at 50 mK. In addition, we identify a regime characterized by h/e-periodic oscillations but with superconductor-like nonlinear transport. Gate-defined superconducting moire devices offer high tunability for probing the nature of superconducting and correlated insulating states. Here, the authors report the Little-Parks and Aharonov-Bohm effects in a single gate-defined magic-angle twisted bilayer graphene device.