Flat Bands in Magic-Angle Bilayer Photonic Crystals at Small Twists

Abstract

The new physics of magic-angle twisted bilayer graphene (TBG) motivated extensive studies of flat bands hosted by moiré superlattices in van der Waals structures, inspiring the investigations into their photonic counterparts with potential applications including Bose-Einstein condensation. However, correlation between photonic flat bands and bilayer photonic moire ´ systems remains unexplored, impeding further development of moire ´ photonics. In this work, we formulate a coupled-mode theory for low-angle twisted bilayer honeycomb photonic crystals as a close analogy of TBG, discovering magic-angle photonic flat bands with a non-Anderson-type localization. Moreover, the interlayer separation constitutes a convenient degree of freedom in tuning photonic moire ´ bands without high pressure. A phase diagram is constructed to correlate the twist angle and separation dependencies to the photonic magic angles. Our findings reveal a salient correspondence between fermionic and bosonic moiré systems and pave the avenue toward novel applications through advanced photonic band or state engineering.

Moiré‐Driven Topological Transitions and Extreme Anisotropy in Elastic Metasurfaces

“…[15,16] These phenomena, at the heart of the thriving field of twistronics, [17] arise from the hybridization of the band structures associated with the two isolated monolayers, and the associated formation of moiré superlattices. Macroscopic-scale implementations of these concepts using phononic and photonic metamaterials [18,19] have demonstrated flat bands in macroscopic analogues of bilayer graphene, [20][21][22][23] field localization within moiré lattices, [24][25][26] the destruction of valley topological protection, [27] artificial gauge fields, [28] and broadband tunable bianisotropy for biosensing applications. [29][30][31] These concepts have also been recently transposed to optical metamaterials, based on extreme anisotropic responses over hyperbolic metasurfaces (HMTs).…”

Photonic Band Gaps and Resonance Modes in 2D Twisted Moiré Photonic Crystal

“…Twisted moiré photonic crystal is an optical analog of twisted 2D materials while photonic crystal is a periodic dielectric structure with a modulation of the refractive index close to the operation wavelength of light [19][20][21]. The twisted bilayer photonic crystal consists of two layers of identical photonic crystal stacked into moiré patterns [19,[22][23][24] that also revealed magic-angle photonic flat bands with a non-Anderson-type localization [23]. Several research groups have generated twisted photonic crystals in photorefractive crystals with a shallow refractive index modulation and have observed the localization and delocalization of light waves [25][26][27][28][29][30][31].…”

Flatband mode in photonic moiré superlattice for boosting second-harmonic generation with monolayer van der Waals crystals

“…The moiré superlattices host exotic electronic states in condensed-matter systems, leading to many salient physical phenomena, such as magic-angle graphene [1], moiré excitons [2], fractional Chern insulator [3], etc. By employing the correspondence between electronic waves and light waves, a surge of effort has been devoted recently to exploring moiré physics in optics [4][5][6][7][8][9][10][11][12][13], showing promising breakthroughs both fundamentally and practically. The flatbands hosted by moiré superlattices is a remarkable feature that can be achieved by tuning the twisting angles ("magic angles" [12]), as well as by scanning the separations between the bilayer photonic slabs ("magic distances" [14]).…”

“…By employing the correspondence between electronic waves and light waves, a surge of effort has been devoted recently to exploring moiré physics in optics [4][5][6][7][8][9][10][11][12][13], showing promising breakthroughs both fundamentally and practically. The flatbands hosted by moiré superlattices is a remarkable feature that can be achieved by tuning the twisting angles ("magic angles" [12]), as well as by scanning the separations between the bilayer photonic slabs ("magic distances" [14]). The flatbands has been reported in mismatched hexagonal-lattice metacrystals [10], twisted bilayer honeycomb photonic crystals [7,12], and mismatched bilayer 1D photonic crystal slabs [14].…”