Tunable quantum interferometer for correlated moir\'e electrons

TL;DR

This paper demonstrates the observation of fundamental quantum coherence effects, the Little-Parks and Aharonov-Bohm effects, in a tunable moiré superconductor device based on magic-angle twisted bilayer graphene, revealing insights into correlated electron states.

Contribution

It introduces a novel gate-defined ring device in MATBG that enables simultaneous observation of multiple quantum coherence phenomena, advancing the study of correlated states in 2D materials.

Findings

Observed Little-Parks effect confirming charge 2e in superconducting phase

Measured coherence length of moiré electrons exceeds a few microns at 50 mK

Identified h/e oscillations with superconductor-like nonlinear transport

Abstract

Magic-angle twisted bilayer graphene (MATBG) can host an intriguing variety of gate-tunable correlated states, including superconducting and correlated insulator states. Junction-based superconducting devices, such as Josephson junctions and SQUIDs, have been introduced recently and enable the exploration of the charge, spin, and orbital nature of superconductivity and the coherence of moir\'e electrons in MATBG. However, complementary fundamental coherence effects - in particular, the Little-Parks effect in a superconducting and the Aharonov-Bohm effect in a normal conducting ring - remained to be observed. Here, we report the observation of both these phenomena in a single gate-defined ring device where we can embed a superconducting or normal conducting ring in a correlated or band insulator. We directly observe the Little-Parks effect in the superconducting phase diagram as a function of density and magnetic field, confirming the effective charge of $2e$. By measuring the Aharonov-Bohm effect, we find that in our device, the coherence length of normal conducting moir\'e electrons exceeds a few microns at 50 mK. Surprisingly, we also identify a regime characterized by $h/e$-periodic oscillations but with superconductor-like nonlinear transport. Taken together, these experiments establish a novel device platform in MATBG, and more generally in tunable 2D materials, to unravel the nature of superconductivity and other correlated quantum states in these materials.