Correlated insulators in twisted mono-mono-bilayer graphene

TL;DR

This study demonstrates how tuning twist angles and displacement fields in twisted mono-mono-bilayer graphene induces various correlated electronic states, including insulators and potential excitonic phases, advancing the understanding of twistronics.

Contribution

It introduces a method to control correlated states in TMMBG by adjusting twist angles and fields, revealing new phases and potential for valleytronics applications.

Findings

Observation of a transition from metallic to valley-polarized insulator at ν = -2

Enhanced effective g-factor correlating with coupling strength

Potential identification of an excitonic insulator candidate

Abstract

Graphene-based moir\'e superlattice featuring flat bands is a promising platform for studying strongly correlated states. By tuning two twist angles and displacement fields in twisted mono-mono-bilayer graphene (TMMBG), we observed a correlated metallic state evolved into a valley-polarized correlated insulator at the filling factor of $\nu = -2$, with the coupling strength between the top two monolayer graphene intensifying. Moreover, the corresponding effective g-factor obtained from fitting the thermal activation gap is enhanced with the coupling strength, suggesting that TMMBG can be harnessed for developing valleytronics devices. In addition, the observation of an unconventional correlated electron-hole insulator suggests that this state might be a candidate for an excitonic insulator, which may generated by the correlation from band nesting, which encourages further research in non-Fermi liquid physics. Our work reveals that tuning multiple twist angles can provide a unique route for studying quantum many-body states in twistronics.