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Replica higher-order topology of Hofstadter butterflies in twisted bilayer graphene

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jats:titleAbstract</jats:title>jats:pThe Hofstadter energy spectrum of twisted bilayer graphene (TBG) is found to have recursive higher-order topological properties. We demonstrate that higher-order topological insulator (HOTI) phases, characterized by localized corner states, occur as replicas of the original HOTIs to fulfill the self-similarity of the Hofstadter spectrum. We show the existence of exact flux translational symmetry in TBG at all commensurate angles. Based on this result, we identify that the original HOTI phase at zero flux is re-entrant at a half-flux periodicity, where the effective twofold rotation is preserved. In addition, numerous replicas of the original HOTIs are found for fluxes without protecting symmetries. Like the original HOTIs, replica HOTIs feature both localized corner states and edge-localized real-space topological markers. The replica HOTIs originate from the different interaction scales, namely, intralayer and interlayer couplings, in TBG. The topological aspect of Hofstadter butterflies revealed in our results highlights symmetry-protected topology in quantum fractals.</jats:p>


Acknowledgements: S.-W.K. thanks Jonah Herzog-Arbeitman for helpful discussions. M.J.P. thanks Jaehoon Kim for providing mathematical insights. This work was supported by the Korean National Research Foundation (NRF) Basic Research Laboratory (NRF-2020R1A4A307970713), the NRF Grant numbers (NRF-2021R1A2C101387112 and NRF-2021M3H3A1038085). This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (RS-2023-00252085, RS-2023-00218998). The computational resource was provided by the Korea Institute of Science and Technology Information (KISTI) (KSC-2020-CRE-0108).


51 Physical Sciences, 5104 Condensed Matter Physics

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npj Computational Materials

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Springer Science and Business Media LLC
National Research Foundation of Korea (NRF) (NRF-2020R1A4A307970713, NRF-2021R1A2C101387112, NRF-2021R1A2C101387112, RS-2023-00218998, RS-2023-00252085, NRF-2020R1A4A307970713, NRF-2021R1A2C101387112, NRF-2021M3H3A1038085)
Korea Institute of Science and Technology Information (KISTI) (KSC-2020-CRE-0108, KSC-2020-CRE-0108, KSC-2020-CRE-0108)