Evidence of Flat Bands and Correlated States in Buckled Graphene Superlattices

TL;DR

This paper demonstrates a new method to create flat electronic bands in buckled graphene monolayers on substrates, leading to correlated electronic states without the need for precise twist-angle tuning.

Contribution

It introduces a buckling-induced flat-band formation in graphene, providing an alternative to twisted bilayer methods for exploring correlated electron phenomena.

Findings

Buckled graphene exhibits flat electronic bands due to substrate-induced buckling.

Electrostatic doping into flat-bands reveals pseudogap-like features indicating correlated states.

The approach enables scalable creation of flat-band systems without fine-tuning twist angles.

Abstract

Two-dimensional atomic crystals can radically change their properties in response to external influences such as substrate orientation or strain, resulting in essentially new materials in terms of the electronic structure. A striking example is the creation of flat-bands in bilayer-graphene for certain 'magic' twist-angles between the orientations of the two layers. The quenched kinetic-energy in these flat-bands promotes electron-electron interactions and facilitates the emergence of strongly-correlated phases such as superconductivity and correlated-insulators. However, the exquisite fine-tuning required for finding the magic-angle where flat-bands appear in twisted-bilayer graphene, poses challenges to fabrication and scalability. Here we present an alternative route to creating flat-bands that does not involve fine tuning. Using scanning tunneling microscopy and spectroscopy, together with numerical simulations, we demonstrate that graphene monolayers placed on an atomically-flat substrate can be forced to undergo a buckling-transition, resulting in a periodically modulated pseudo-magnetic field, which in turn creates a post-graphene material with flat electronic bands. Bringing the Fermi-level into these flat-bands by electrostatic doping, we observe a pseudogap-like depletion in the density-of-states, which signals the emergence of a correlated-state. The described approach of 2D crystal buckling offers a strategy for creating other superlattice systems and, in particular, for exploring interaction phenomena characteristic of flat-bands.