High-order nonlinear optical response of a twisted bilayer graphene

Ikeda, Tatsuhiko

doi:10.1103/physrevresearch.2.032015

Cited by 33 publications

(17 citation statements)

References 76 publications

(86 reference statements)

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“…The quenching of the kinetic energy of flatband 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

et al. 2021

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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 intraband quantum metric allows diamagnetic coupling inside a flat band; the interband 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 twist-angle 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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Section: Introductionmentioning

confidence: 99%

Light-matter coupling and quantum geometry in moiré materials

et al. 2021

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“…The periodicity and electrical and optoelectronic properties of TBG completely depend on the twist angle between the upper and lower layers, which makes TBG show magical and revolutionary novel characteristics in terms of electricity, optics, and heat. The TBG exhibits an abundance of high-harmonic in the intense laser fields, suggesting nonlinear “optotwistronics”, i.e., artificial twists to control the optical properties of the layered material [ 16 ]. In the TBG, some components of the nonlinear photoconductivity tensor are proportional to the orbital magnetization of the system, which would exhibit significant hysteresis behavior in the presence of a perpendicular magnetic field [ 17 ].…”

Section: Introductionmentioning

confidence: 99%

Electric Field Induced Twisted Bilayer Graphene Infrared Plasmon Spectrum

et al. 2021

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In this work, we investigate the role of an external electric field in modulating the spectrum and electronic structure behavior of twisted bilayer graphene (TBG) and its physical mechanisms. Through theoretical studies, it is found that the external electric field can drive the relative positions of the conduction band and valence band to some extent. The difference of electric field strength and direction can reduce the original conduction band, and through the Fermi energy level, the band is significantly influenced by the tunable electric field and also increases the density of states of the valence band passing through the Fermi level. Under these two effects, the valence and conduction bands can alternately fold, causing drastic changes in spectrum behavior. In turn, the plasmon spectrum of TBG varies from semiconductor to metal. The dielectric function of TBG can exhibit plasmon resonance in a certain range of infrared.

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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.

show abstract

High-order nonlinear optical response of a twisted bilayer graphene

Cited by 33 publications

References 76 publications

Light-matter coupling and quantum geometry in moiré materials

Light-matter coupling and quantum geometry in moiré materials

Electric Field Induced Twisted Bilayer Graphene Infrared Plasmon Spectrum

Light-matter coupling and quantum geometry in moiré materials

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