Tiancheng Zhang1,3,Kaichen Dong1,2,Jiachen Li1,2,Qingjun Wang1,Fuyi Yang1,Yoonsoo Rho1,Danqing Wang1,2,Costas Grigoropoulos1,Junqiao Wu1,2,Jie Yao1,2
University of California, Berkeley1,Lawrence Berkeley National Laboratory2,Peking University3
Tiancheng Zhang1,3,Kaichen Dong1,2,Jiachen Li1,2,Qingjun Wang1,Fuyi Yang1,Yoonsoo Rho1,Danqing Wang1,2,Costas Grigoropoulos1,Junqiao Wu1,2,Jie Yao1,2
University of California, Berkeley1,Lawrence Berkeley National Laboratory2,Peking University3
The new physics of magic-angle effects in twisted bilayer graphene motivated vast investigation into the flat bands hosted by van der Waals moiré structures. Considering the unique correspondence between condensed matter systems and photonic systems, it is important to study the photonic counterparts of twisted bilayer graphene with potential applications including Bose-Einstein condensation. However, the correlation between photonic flat bands and bilayer photonic moiré systems lacks in-depth formulation, impeding further development of moiré photonics. Here, we report a theoretical model of low-angle twisted bilayer honeycomb photonic crystals with a subwavelength interlayer separation (as a close analogy of twisted bilayer graphene). A coupled mode theory is used to describe the crosstalk among photonic units, followed by a continuum model of optical modes. Using our theoretical description, we discover magic-angle photonic flat bands with spiky photonic density of states. A phase diagram is constructed to correlate the twist angle and interlayer separation dependencies to the photonic magic angles. Full-wave simulation is conducted to verify the theoretical model, resolving that non-Anderson-type light localization exists in the AA regions at the 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.