Topological flat bands and correlated states in twisted monolayer-bilayer graphene

Abstract

Monolayer graphene placed with a twist on top of AB-stacked bilayer graphene hosts topological flat bands in a wide range of twist angles. The dispersion of these bands and gaps between them can be efficiently controlled by a perpendicular electric field, which induces topological transitions accompanied by changes of the Chern numbers. In the regime where the applied electric field induces gaps between the flat bands, we find a relatively uniform distribution of the Berry curvature. Consequently, interaction-induced valley-and/or spin-polarized states at integer filling factors are energetically favorable. In particular, we predict a quantum anomalous Hall state at filling factors ν = 1, 3 for a range of twist angles 1 • < θ < 1.4 •. Furthermore, to characterize the response of the system to magnetic field, we computed the Hofstadter butterfly and the Wannier plot, which can be used to probe the dispersion and topology of the flat bands in this material.

Competing correlated states and abundant orbital magnetism in twisted monolayer-bilayer graphene

“…4 ∘14-16 . The absence of robust correlated insulating states is likely a consequence of the larger bandwidth compared with the D > 0 bands [17][18][19] . Supplementary Note 4 and Supplementary Table 1 provide a detailed summary of the correlated states observed in our three devices, as well as those previously reported in refs.…”

“…The bandwidth, W, and valley Chern number, C v , additionally depend on the orientation of D (Supplementary Fig. 1) [17][18][19] , which can polarize charge carriers more strongly towards either the monolayer or Bernal-stacked bilayer graphene sheet 14 . The high tunability of the bands with the combination of twist angle, doping, D, and magnetic field makes tMBG an attractive platform for investigating the nature of closely competing correlated and topological ground states.…”

Moire Band Structures of the Double twisted Few Layer Graphene

“…A good analogy in single twist devices is the relation among the TBG, twisted double-bilayer graphene (TDBG) [48][49][50][51][52][53][54][55][56] and twisted TLG (i.e. twisted monolayer-bilayer graphene) [57][58][59][60][61][62][63][64][65] . It is known that, once the MLGs in the TBG are replaced by BLG, similar but different moiré flat band structures are achieved 49,57,66 .…”

Moire flat bands in twisted 2D hexagonal vdW material

“…Following the success of TBG, a number of new moiré flatband systems beyond TBG are explored, from the homobilayers, heterobilayers to multilayers configurations, including trilayer Graphene/hBN [36,37], twisted double bilayer graphene [38][39][40][41][42][43][44], twisted trilayer graphene [45][46][47], twisted monolayer-bilayer graphene [48][49][50][51] and twisted transition metal dichalcogenides (TMDs) [52][53][54][55][56][57][58] and so on. For example, Dai et al [59] theoretically studied stacking configurations by the generic form of (M + N)-layers TBG, where the N-layers graphene are stacked on top of M-layers graphene at a small twist angle and explore their electronic structures and topological properties.…”