Flat-band driven ordered magnetism in sp3 supermodulated defected fluorinated graphene

Abstract

Strong correlation drives a variety of exotic quantum phases, and thus has been a vital topic in modern condensed matter physics. One of the recent advances is the strong correlations in flat-band systems. Here, by introducing the supermodulations of sp${}^3$ fluorinated islands around divacancy, a new strategy to enhance the correlations of the $\pi$ electrons in defected graphene, beyond the moiré patterns, is proposed. Ab-initio calculations reveal that the systems host nearly flat band, and the flatness of the band near the Fermi level is substantially strengthened, being comparable to that in small angle twisted bilayer graphene. Interestingly, the topography of the effective model can be tuned by properly removing the fluorine atoms in the island. Consequently, the long-range ordered magnetic ground states appear in the designed structures as theoretically predicted and experimentally observed, confirming the validity of this new supermodulation. We show that the origin of magnetism is from the fluorine decorated to the defected graphene, and the periodic network among the $\pi$ electrons of carbon is responsible for the magnetic long range ordering in the fluorinated reduced graphene. This work provides a feasible and simple platform to study the interaction induced phenomena in defected graphene. Moreover, the much reduced supercell size, in comparison with the moiré materials, may support higher Curie temperature, opening an avenue for future high-temperature spintronics applications in graphene-based materials.