Evidence of Flat Bands and Correlated States in Buckled Graphene Superlattices

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.

22 pages, 15 figures. arXiv admin note: substantial text overlap with arXiv:1904.10147

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• Origami-controlled strain engineering of tunable flat bands and correlated states in folded graphene
• Giant periodic pseudo-magnetic fields in strained kagome magnet FeSn epitaxial films on SrTiO${}_3$(111) substrate
• Isolated flat bands in an interlocking-circles lattice
• Quantum Monte Carlo study of honeycomb antiferromagnets under a triaxial strain
• Emergence of strain-induced moiré patterns and pseudo-magnetic field confined states in graphene
• Hofstadter butterflies in magnetically modulated graphene bilayer: an algebraic approach