Slave-rotor theory on magic-angle twisted bilayer graphene

Shin-Ming Huang^1*, Yi-Ping Huang², Ting-Kuo Lee¹

¹Department of Physics, National Sun Yat-sen University, Kaohsiung, Taiwan
²Condensed Matter Theory Group, Paul Scherrer Institute, Villigen, Switzerland

* Presenter:Shin-Ming Huang, email:shinming@mail.nsysu.edu.tw

We study the strongly correlated electronic system for the fidget-spinner-like orbitals in magic-angle twisted bilayer graphene. Due to the extended Wannier orbitals, there are interactions between orbitals at different hexagons, the two-orbital cluster Hubbard model is considered. We use the slave-rotor mean-field theory to study the model and focus around half filling of valence bands below the neutrality point. The theory shows relatively impotent long-range hopping after renormalization and predicts multiple Mott insulator phases at fractional filling, not only for integer charges per moire site. With the Kekule valence bond order, the Mott insulator phases are extended away from the factional filling. Considering second-order perturbation, spin- valley fluctuations give rise to the pairing attraction, exhibiting superconducting domes adjacent to Mott insulator phases. The cluster interaction generates high entanglement among clusters, implying plenty of possibilities of nontrivial states.`

Keywords: twisted bilayer graphene, slave rotor, Kekule valence bond order, Mott insulator , superconductivity