We theoretically study the Hofstadter butterfly of a triangular network model in minimally twisted bilayer graphene. The band structure manifests periodicity in energy, mimicking that of Floquet systems. The butterfly diagrams provide fingerprints of the model parameters and reveal the hidden band topology. In a strong magnetic field, we establish that minimally twisted bilayer graphene realizes low-energy Floquet topological insulators (FTIs) carrying zero Chern number, while hosting chiral edge states in bulk gaps. We identify the FTIs by analyzing the nontrivial spectral flow in the Hofstadter butterfly, and by explicitly computing the chiral edge states. Our theory paves the way for an effective practical realization of FTIs in equilibrium solid-state systems.
Yang-Zhi Chou is currently a postdoc fellow in the Condensed Matter Theory Center, University of Maryland College Park. He is working on quantum material theory including topological phases, disordered systems, and strongly correlated physics. He graduated from Rice University in 2016. During 2016 to 2019, he was a postdoc fellow in the University of Colorado Boulder.
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