Interaction-driven band flattening and correlated phases in magic-angle graphene superlattices

Flat electronic bands, characteristic of 'magic-angle' twisted bilayer and trilayer graphene, host many correlated phenomena. Nevertheless, many properties of flat bands and emerging symmetry-broken phases in these systems are still poorly understood. In this talk, I will discuss scanning tunneling microscopy experiments that examine filling-dependent band deformations in these systems and emerging correlated phases. In bilayers, we observe flattening of the bands that is appreciable even when the angle is well above the magic angle value, and so the material is nominally in a weakly correlated regime. In trilayers, we additionally see significant shifting between flat and Dirac-like bands. Our observations are consistent with a model that suggests that a substantial enhancement of the density of states caused by the band flattening triggers a cascade of symmetry-breaking transitions. In the second part of the talk, I will discuss recent insights into correlated phases emerging from these band structure effects.