A Tunable Monolithic Superconducting Quantum Interference Device in Twisted Bilayer Graphene

We present a Superconducting Quantum Interference Device (SQUID) in Magic-Angle Twisted Bilayer Graphene (MATBG) [1], building on previous single-junction realizations [2, 3]. The superconducting phase difference is controlled through the magnetic field. We observe magneto-oscillations of the critical current, demonstrating long-range coherence agreeing with an effective charge of 2e for the superconducting charge carriers. We tune to both asymmetric and symmetric SQUID configurations by electrostatically controlling the critical currents through the junctions. With this tunability, we study the inductances in the device, finding values above 100nH. Furthermore, we directly observe the current-phase relation of one of the Josephson junctions of the device.

[1] Cao, Y. et al. Unconventional superconductivity in magic-angle graphene superlattices. Nature 556, 43–50 (2018)

[2] de Vries, F.K. et al. Gate-defined Josephson junctions in magic-angle twisted bilayer graphene. Nat. Nanotechnol. 16, 760–763 (2021)

[3] Rodan-Legrain, et al. Highly tunable junctions and non-local Josephson effect in magic-angle graphene tunnelling devices. Nat. Nanotechnol. 16, 769–775 (2021)

[4] Portolés, E. et al. A Tunable Monolithic SQUID in Twisted Bilayer Graphene. arXiv:2201.13276 (2022)