Emergence of Chern Insulating States in Non-Magic Angle Twisted Bilayer Graphene

Twisting two layers into a magic angle (MA) of ∼1.1° is found essential to create low energy flat bands and the resulting correlated insulating, superconducting, and magnetic phases in twisted bilayer graphene (TBG). While most of previous works focus on revealing these emergent states in MA-TBG, a study of the twist angle dependence, which helps to map an evolution of these phases, is yet less explored. Here, we report a magneto-transport study on one non-magic angle TBG device, whose twist angle θ changes from 1.25° at one end to 1.43° at the other. For θ = 1.25° we observe an emergence of topological insulating states at hole side with a sequence of Chern number | C | = 4 – | v |, where v is the number of electrons (holes) in moiré unite cell. When θ > 1.25°, the Chern insulator from flat band disappears and evolves into fractal Hofstadter butterfly quantum Hall insulator where magnetic flux in one moiré unite cell matters. Our observations will stimulate further theoretical and experimental investigations on the relationship between electron interactions and non-trivial band topology. (express letter)