Untwisting Moire Physics: Almost Ideal Bands and Fractional Chern Insulators in Periodically Strained Monolayer Graphene

Moire systems have emerged in recent years as a rich platform to study strong correlations. Here, we will propose a simple, experimentally feasible setup based on periodically strained graphene that reproduces several key aspects of twisted moire heterostructures-but without introducing a twist. We consider a monolayer graphene sheet subject to a C-2-breaking periodic strain-induced pseudomagnetic field with period L-M >> a, along with a scalar potential of the same period. This system has almost ideal flat bands with valley-resolved Chern number +/- 1, where the deviation from ideal band geometry is analytically controlled and exponentially small in the dimensionless ratio (L-M/l(B))(2), where l(B) is the magnetic length corresponding to the maximum value of the pseudomagnetic field. Moreover, the scalar potential can tune the bandwidth far below the Coulomb scale, making this a very promising platform for strongly interacting topological phases. Using a combination of strong-coupling theory and self-consistent Hartree-Fock, we find quantum anomalous Hall states at integer fillings. At fractional filling, exact diagonaliztion reveals a fractional Chern insulator at parameters in the experimentally feasible range. Overall, we find that this system has larger interaction-induced gaps, smaller quasiparticle dispersion, and enhanced tunability compared to twisted graphene systems, even in their ideal limit.

Automated summary

This article proposes a setup based on periodically strained graphene that reproduces key aspects of twisted moire heterostructures. The system has almost ideal flat bands with valley-resolved Chern number +/- 1, exhibiting larger interaction-induced gaps and smaller quasiparticle dispersion compared to twisted graphene systems.