Reentrant Correlated Insulators in Twisted Bilayer Graphene at 25T ($2\ddot{I}€$ Flux)

Abstract

Twisted bilayer graphene (TBG) is remarkable for its topological flat bands, which drive strongly-interacting physics at integer fillings, and its simple theoretical description facilitated by the Bistritzer-MacDonald Hamiltonian, a continuum model coupling two Dirac fermions. Due to the large moiré unit cell, TBG offers the unprecedented opportunity to observe reentrant Hofstadter phases in laboratory-strength magnetic fields near $25$T. This Letter is devoted to magic angle TBG at $2\ddot{I}€$ flux where the magnetic translation group commutes. We use a newly developed gauge-invariant formalism to determine the exact single-particle band structure and topology. We find that the characteristic TBG flat bands reemerge at $2\ddot{I}€$ flux, but, due to the magnetic field breaking $C_{2z}\mathcal{T}$, they split and acquire Chern number $\pm 1$. We show that reentrant correlated insulating states appear at $2\ddot{I}€$ flux driven by the Coulomb interaction at integer fillings, and we predict the characteristic Landau fans from their excitation spectrum. We conjecture that superconductivity can also be re-entrant at $2\ddot{I}€$ flux.

(See also "Observation of re-entrant correlated insulators and interaction driven Fermi surface reconstructions at one magnetic flux quantum per moire unit cell in magic-angle twisted bilayer graphene" by Das et al.)