Topological phase diagram of twisted bilayer graphene as a function of the twist angle

TL;DR

This paper explores how varying the twist angle in twisted bilayer graphene influences its electronic phases, revealing multiple topological transitions and novel Chern number states driven by band hybridization and inversions.

Contribution

It provides a detailed analysis of topological phase transitions in TBG as a function of twist angle, including the discovery of new Chern number phases.

Findings

Multiple topological phase transitions identified

Central bands can have Chern number C=2

Band inversions drive topological changes

Abstract

Twisted bilayer graphene (TBG) hosts a rich landscape of electronic phases arising from the interplay between strong electron-electron interactions and nontrivial band topology. While the flat bands near zero energy are central to many correlated phenomena, their interaction with higher-energy remote bands remains less understood. Here, we investigate these hybridization processes as a function of the twist angle and analyze their impact on the charge distribution, topological properties such as Chern number, quantum metric, and orbital magnetic energy. We identify multiple topological phase transitions between magic angles, driven by band inversions at high-symmetry points in momentum space. Notably, the central bands can exhibit phases with Chern numbers C = 2, revealing previously unreported topological states in TBG.