A family of ideal Chern flat bands with arbitrary Chern number in chiral twisted graphene multilayers

TLDR: In this article, a family of twisted bilayer graphene (CTBG) multilayers with a single twist on top of the stacked layers was considered, and it was shown that the Berry curvature distribution can be continuously tuned while maintaining perfect quantum geometry.

Abstract: We consider a family of twisted graphene multilayers consisting of $n$-untwisted {chirally stacked layers, e.g. AB, ABC, etc,} with a single twist on top of $m$-untwisted {chirally stacked} layers. Upon neglecting both trigonal warping terms for the untwisted layers and the same sublattice hopping between all layers, the resulting models generalize several remarkable features of the chiral model of twisted bilayer graphene (CTBG). {In particular, they exhibit a set of magic angles which are identical to those of CTBG at which a pair of bands (i) are perfectly flat, (ii) have Chern numbers in the sublattice basis given by $\pm (n,-m)$ or $\pm (n+m-1,-1)$ depending on the stacking chirality, and (iii) satisfy the trace condition, saturating an inequality between the quantum metric and the Berry curvature, and thus realizing ideal quantum geometry}. We provide explicit analytic expressions for the flat band wavefunctions at the magic angle in terms of the CTBG wavefunctions. We also show that the Berry curvature distribution in these models can be continuously tuned while maintaining perfect quantum geometry. Similar to the study of fractional Chern insulators in ideal $C = 1$ bands, these models pave the way for investigating exotic topological phases in higher Chern bands for which no Landau level analog is available.