上海科技大学知识管理系统

Twisting two layers into a magic angle (MA) of similar to 1.1 degrees 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 theta changes from 1.25 degrees at one end to 1.43 degrees at the other. For theta = 1.25 degrees 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 moire unite cell. When theta > 1.25 degrees, the Chern insulator from flat band disappears and evolves into fractal Hofstadter butterfly quantum Hall insulator where magnetic flux in one moire unite cell matters. Our observations will stimulate further theoretical and experimental investigations on the relationship between electron interactions and non-trivial band topology.