Moir\'e fractals in twisted graphene layers

Abstract

Twisted bilayer graphene (TBLG) subject to a sequence of commensurate external periodic potentials reveals the formation of moir\'{e} fractals (MF) that share striking similarities with the central place theory (CPT) of economic geography, thus uncovering a remarkable connection between twistronics and the geometry of economic zones. MFs arise from the self-similarity of the emergent hierarchy of Brillouin zones (BZ), forming a nested subband structure within the bandwidth of the original moir\'{e} bands. We derive the fractal generators (FG) for TBLG under these external potentials and explore their impact on the hierarchy of the BZ edges and the wavefunctions at the Dirac point. By examining realistic super-moir\'{e} structures (SMS) and demonstrating their equivalence to MFs with periodic perturbations under specific conditions, we establish MFs as a general description for such systems. Furthermore, we uncover parallels between the modification of the BZ hierarchy and magnetic BZ formation in Hofstadter's butterfly (HB), allowing us to construct an incommensurability measure for MFs \textit{vs.} twist angle. The resulting bandstructure hierarchy bolsters correlation effects, pushing more bands within the same energy window for both commensurate and incommensurate TBLG.