Decoupling superconductivity and correlated insulators in twisted bilayer graphene

TL;DR

This paper demonstrates that in twisted bilayer graphene, superconductivity can occur independently of correlated insulating states, indicating they originate from different mechanisms despite their proximity near the flat band condition.

Contribution

It provides evidence that superconductivity and correlated insulators in twisted bilayer graphene are decoupled phenomena, challenging the assumption of a direct causal relationship.

Findings

Superconductivity persists beyond the angle range where correlated insulators are observed.

Superconductivity and insulating states are strongest near the flat band but can occur separately.

Results support a 'competing phases' model with distinct origins for each state.

Abstract

When bilayer graphene is rotationally faulted to an angle $\theta\approx 1.1^\circ$, theory predicts the formation of a flat electronic band and correlated insulating, superconducting, and ferromagnetic states have all been observed at partial band filling. The proximity of superconductivity to correlated insulators has suggested a close relationship between these states, reminiscent of the cuprates where superconductivity arises by doping a Mott insulator. Here, we show that superconductivity can appear without correlated insulating states. While both superconductivity and correlated insulating behavior are strongest near the flat band condition, superconductivity survives to larger detuning of the angle. Our observations are consistent with a "competing phases" picture, in which insulators and superconductivity arise from disparate mechanisms.