Valley-selective Floquet Chern Flat Bands in Twisted Multilayer Graphene

Lu, Ming; Zeng, Jiang; Liu, Haiwen; Gao, Jin-Hua; Xie, X. C.

doi:10.48550/arxiv.2007.15489

Cited by 1 publication

(1 citation statement)

References 46 publications

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“…The quenching of the kinetic energy of flat-band electrons might allow one to reach the regime of strong LMC more easily than in strongly dispersive materials [40]. Specifically for TBG and other moiré systems, there have been first theoretical explorations of Floquet engineering [129][130][131][132][133][134][135][136][137] and nonlinear optical responses [138]. Recently a measured strong mid-infrared photoresponse in bilayer graphene at small twist angles was reported [139].…”

Section: Introductionmentioning

confidence: 99%

Light-matter coupling and quantum geometry in moiré materials

Topp,

Eckhardt,

Kennes

et al. 2021

Preprint

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Quantum geometry has been identified as an important ingredient for the physics of quantum materials and especially of flat-band systems, such as moiré materials. On the other hand, the coupling between light and matter is of key importance across disciplines and especially for Floquet and cavity engineering of solids. Here we present fundamental relations between light-matter coupling and quantum geometry of Bloch wave functions, with a particular focus on flat-band and moiré materials, in which the quenching of the electronic kinetic energy could allow one to reach the limit of strong light-matter coupling more easily than in highly dispersive systems. We show that, despite the fact that flat bands have vanishing band velocities and curvatures, light couples to them via geometric contributions. Specifically, the intra-band quantum metric allows diamagnetic coupling inside a flat band; the inter-band Berry connection governs dipole matrix elements between flat and dispersive bands. We illustrate these effects in two representative model systems: (i) a sawtooth quantum chain with a single flat band, and (ii) a tight-binding model for twisted bilayer graphene. For (i) we highlight the importance of quantum geometry by demonstrating a nonvanishing diamagnetic light-matter coupling inside the flat band. For (ii) we explore the twistangle dependence of various light-matter coupling matrix elements. Furthermore, at the magic angle corresponding to almost flat bands, we show a Floquet-topological gap opening under irradiation with circularly polarized light despite the nearly vanishing Fermi velocity. We discuss how these findings provide fundamental design principles and tools for light-matter-coupling-based control of emergent electronic properties in flat-band and moiré materials.

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