Signature of gate tunable superconducting network in twisted bilayer graphene

TL;DR

This study uses scanning tunneling microscopy to observe how gate voltage controls superconductivity in twisted bilayer graphene, revealing a transition from partial to full superconducting states and uncovering spatial pairing behaviors.

Contribution

It provides the first microscopic imaging of gate-tunable superconducting networks in twisted bilayer graphene, highlighting the spatial hierarchy of pairing and phase evolution.

Findings

Partial superconductivity in under-doped regime with non-gapped regions.

Full superconductivity at optimal doping with modulated gap sizes.

Observation of a spatial hierarchy in pairing behavior.

Abstract

Twisted van der Waals materials provide a tunable platform for investigating two-dimensional superconductivity and quantum phases. Using spectra-imaging scanning tunneling microscopy, we study the superconducting states in twisted bilayer graphene and track their evolution from insulating phases. Gate-dependent spectroscopic measurements reveal two distinct regimes: under-doped ({\nu} = -2.3) and optimally doped ({\nu} = -2.6). In the under-doped regime, partial superconductivity arises, forming a network interspersed with non-gapped regions. At optimal doping, the entire unit cell demonstrates superconductivity, with gap size modulation showing an anti-correlation with the local density of states. This gate-dependent transition from an insulating phase to a modulated superconductor uncovers an unexpected spatial hierarchy in pairing behavior and offers direct microscopic insights to constrain theories of superconductivity in moir\'e systems.