2021/05/27 by Zhang, Kevin, Yang Zhang, Liang Fu +4
Materials Science · Physics and Astronomy · #FOS: Physical sciences #Graphene research and applications #Mesoscale and Nanoscale Physics (cond-mat.mes-hall) #Physics of Superconductivity and Magnetism #Quantum and electron transport phenomena
paper · pdf · doi:10.48550/arxiv.2105.13371
openalex publication_date 2021/05/27 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Although much progress has been made on the physics of magic angle twisted bilayer graphene at integer fillings, little attention has been given to fractional fillings. Here we show that the three-peak structure of Wannier orbitals, dictated by the symmetry and topology of flat bands, facilitates the emergence of a novel state at commensurate fractional filling of ν= n ± 1/3. We dub this state a "fractional correlated insulator". Specifically for the filling of ± 1/3 electrons per moiré unit cell, we show that short-range interactions alone imply an approximate extensive entropy due to the "breathing" degree of freedom of an irregular honeycomb lattice that emerges through defect lines. The leading further-range interaction lifts this degeneracy and selects a novel ferromagnetic nematic state that breaks AB/BA sublattice symmetry. The proposed fractional correlated insulating state might underlie the suppression of superconductivity at ν= 2-1/3 filling observed in arXiv:2004.04148. Further investigation of the proposed fractional correlated insulating state would open doors to new regimes of correlation effects in MATBG.