Unconventional Flat Chern Bands and 2e Charges in Skyrmionic Moire Superlattices

The interplay of topological characteristics in real space and reciprocal space can lead to the emergence of unconventional topological phases. In this Letter, we implement a novel mechanism for generating higher-Chern flat bands on the basis of twisted bilayer graphene (TBG) coupled to topological magnetic structures in the form of the skyrmion lattice. In particular, we discover a scenario for generating vertical bar C vertical bar = 2 dispersionless electronic bands when the skyrmion periodicity and the moire ' periodicity match. Following the Wilczek argument, the statistics of the charge-carrying excitations in this case is bosonic, characterized by electronic charge Q = 2e, which is even in units of electron charge e. The skyrmion coupling strength triggering the topological phase transition is realistic, with its lower bound estimated as 4 meV. The Hofstadter butterfly spectrum results in an unexpected quantum Hall conductance sequence +/- 2e(2)/h, +/- 4e(2)/h, ... for TBG with the skyrmion order.

Automated summary

In this study, we propose a novel mechanism for generating higher-Chern flat bands using twisted bilayer graphene (TBG) coupled with topological magnetic structures known as the skyrmion lattice. By matching the periodicities of the skyrmion and the moire pattern, we discover the emergence of dispersionless electronic bands with vertical bar C vertical bar = 2. The statistics of the charge-carrying excitations in this case follow bosonic behavior, with Q = 2e, indicating even units of electron charge. The realistic lower bound of the skyrmion coupling strength for triggering the topological phase transition is estimated to be 4 meV. The presence of the skyrmion order in TBG leads to an unexpected quantum Hall conductance sequence of +/- 2e(2)/h, +/- 4e(2)/h, ... in the Hofstadter butterfly spectrum.