Highly Tunable Junctions and Nonlocal Josephson Effect in Magic Angle Graphene Tunneling Devices

TL;DR

This paper demonstrates the creation of highly tunable Josephson junctions and tunneling devices within magic-angle twisted bilayer graphene, enabling versatile quantum device functionalities through electrostatic control.

Contribution

It introduces a multi-gated, all-MATBG device platform that allows independent tuning of Josephson junction components and demonstrates nonlocal superconducting effects and single-electron transistor operation.

Findings

MATBG Josephson junctions exhibit nonlocal electrodynamics consistent with Pearl theory.

The devices enable edge tunneling spectroscopy and energy spectrum measurement in the superconducting phase.

Double barrier configurations function as single-electron transistors with Coulomb blockade.

Abstract

Magic-angle twisted bilayer graphene (MATBG) has recently emerged as a highly tunable two-dimensional (2D) material platform exhibiting a wide range of phases, such as metal, insulator, and superconductor states. Local electrostatic control over these phases may enable the creation of versatile quantum devices that were previously not achievable in other single material platforms. Here, we exploit the electrical tunability of MATBG to engineer Josephson junctions and tunneling transistors all within one material, defined solely by electrostatic gates. Our multi-gated device geometry offers complete control over the Josephson junction, with the ability to independently tune the weak link, barriers, and tunneling electrodes. We show that these purely 2D MATBG Josephson junctions exhibit nonlocal electrodynamics in a magnetic field, in agreement with the Pearl theory for ultrathin superconductors. Utilizing the intrinsic bandgaps of MATBG, we also demonstrate monolithic edge tunneling spectroscopy within the same MATBG devices and measure the energy spectrum of MATBG in the superconducting phase. Furthermore, by inducing a double barrier geometry, the devices can be operated as a single-electron transistor, exhibiting Coulomb blockade. These MATBG tunneling devices, with versatile functionality encompassed within a single material, may find applications in graphene-based tunable superconducting qubits, on-chip superconducting circuits, and electromagnetic sensing in next-generation quantum nanoelectronics.