Correlated Insulating and Superconducting States in Twisted Bilayer Graphene Below the Magic Angle

TL;DR

This study reports the observation of both superconducting and insulating states in twisted bilayer graphene with a twist angle below the traditional magic angle, expanding understanding of correlated phenomena in this material.

Contribution

It demonstrates correlated insulating and superconducting states at a smaller twist angle than previously thought, challenging existing theories about the magic angle range.

Findings

Observation of a correlated insulating state at ±5 electrons per moire unit cell.

Detection of superconductivity at a twist angle of approximately 0.93 degrees.

Evidence that the magic angle range in tBLG is larger than previously believed.

Abstract

The emergence of flat bands and correlated behaviors in 'magic angle' twisted bilayer graphene (tBLG) has sparked tremendous interest, though many aspects of the system are under intense debate. Here we report observation of both superconductivity and the Mott-like insulating state in a tBLG device with a twist angle of approximately 0.93, which is smaller than the magic angle by 15%. At an electron concentration of +/-5 electrons per moire unit cell, we observe a narrow resistance peak with an activation energy gap of approximately 0.1 meV, indicating the existence of an additional correlated insulating state. This is consistent with theory predicting the presence of a high-energy band with an energetically flat dispersion. At a doping of +/-12 electrons per moire unit cell we observe a resistance peak due to the presence of Dirac points in the spectrum. Our results reveal that the magic range of tBLG is in fact larger than what is previously expected, and provide a wealth of new information to help decipher the strongly correlated phenomena observed in tBLG.