---

Abstract:

Magic angle twisted bilayer graphene (MATBG) exhibits a variety of gate-tunable correlated states, including superconductor and correlated insulator. Towards the understanding of charge, spin, and orbit nature of superconductivity and the coherence of moiré electrons, gate-defined devices such as Josephson junctions [1] and SQUIDs [2] have been realized. However, the complementary and fundamental coherence effects, namely the Little-Parks effect in superconducting and the Aharonov-Bohm effect in the normal conducting ring have yet to be observed.

Here, we develop a gate-defined ring in which a superconducting or normal conducting loop is surrounded  by a correlated or band insulator [3]. This enables a direct observation of the Little-Parks effect in the superconducting phase diagram as a function of density and magnetic field, confirming the effective charge of 2e. We also determine the coherence length of normal conducting moiré electrons exceeding a few microns at 50 mK via the Aharonov-Bohm effect. Surprisingly, we find a regime that exhibits h/e-periodic oscillations but accompanied by a superconducting-like nonlinear transport. This work provides a new device platform in MATBG and tunable 2D materials, in general, to unravel the nature of superconductivity and other correlated states.

 

[1] F. de Vries et al., Nat. Nanotechnol. 16, 760–763 (2021).

[2] E. Portolés, S. Iwakiri, et al., Nat. Nanotechnol. 17, 1159–1164 (2022).

[3] S. Iwakiri, A. Mestre Torà, et al., submitted.

---