Strongly correlated Hofstadter subbands in minimally twisted bilayer graphene

TL;DR

This paper demonstrates the emergence of strongly correlated Hofstadter subbands and correlated insulating states in minimally twisted bilayer graphene at a non-magic angle under high magnetic flux, revealing new quantum phases.

Contribution

It uncovers the formation of gapped Hofstadter subbands and correlated insulating states in non-magic-angle twisted bilayer graphene through high magnetic field experiments.

Findings

Gapped Hofstadter subbands observed at large magnetic flux.

Correlated insulating states with isospin symmetry breaking.

Enhanced Coulomb interactions dominate over kinetic energy.

Abstract

Moir\'e superlattice in twisted bilayer graphene has been proven to be a versatile platform for exploring exotic quantum phases. Extensive investigations have been invoked focusing on the zero-magnetic-field phase diagram at the magic twist angle around $\theta=1.1\degree$, which has been indicated to be an exclusive regime for exhibiting flat band with the interplay of strong electronic correlation and untrivial topology in the experiment so far. In contrast, electronic bands in non-magic-angle twisted bilayer graphene host dominant electronic kinetic energy compared to Coulomb interaction. By quenching the kinetic energy and enhancing Coulomb exchange interactions by means of an applied perpendicular magnetic field, here we unveil gapped flat Hofstadter subbands at large magnetic flux that yield correlated insulating states in minimally twisted bilayer graphene at $\theta=0.41\degree$. These states appear with isospin symmetry breaking due to strong Coulomb interactions. Our work provides a platform for studying the phase transition of the strongly correlated Hofstadter spectrum.