1. Magic configurations in moire superlattice of bilayer photonic crystal: almost-perfect flatband and unconventional localization

Hai Son Nguyen

Ecole Centrale de Lyon, France

17 June 2021 Thu 5 pm

                                      IBS Center for Theoretical Physics of Complex Systems (PCS), Administrative Office (B349), Theory Wing, 3rd floor

                                      Expo-ro 55, Yuseong-gu, Daejeon, South Korea, 34126 Tel: +82-42-878-8633                     

Moiré structure has been of central interest in fundamental physics during the last few years. The discovery of flatband in moiré patterns emerged when two graphene layers are overlapped at certain at magic twisted angles has led to non-conventional superconductivity and strongly correlating insulator states with nontrivial topology properties. Motivated by the electronic magic angles, since 2020, photonic moiré has attracted tremendous research in light of shaping novel optical phenomena. [1]

In this presentation, I will present  a theoretical study of photonic band structures in moiré patterns that emerged when two mismatched 1D photonic crystal slabs are overlapped. Despite its simplicity, this 1D setup displays analogíes with most of interesting physics of moiré systems from twisted two-dimensional materials. The superlattice eigenmodes are described by an effective four-component Hamiltonian. Accompanying the analytical theory, numerical electromagnetic simulations are performed with a case study of silicon structures operating at telecom wavelength. All numerical simulations are nicely reproduced by the effective Hamiltonian method with high accuracy without any fitting parameters. The obtained band structure are resulted from an interplay between intra-layer and inter-layer coupling mechanisms which is tuned via the distance separating the two layers. Importantly, series of magic distances corresponding to the emergence of almost-perfect photonic flatbands within the whole Brillouin zone are demonstrated. The minibands of moiré superlattice can be described by a single-band tight-binding model with Wannier function tightly confined within a moiré period. The tunnelling rate of light between nearest neighbor Wannier states is continuously modulated by the inter-layer distance and vanished at magic distances, leading to flatband formation and photonic localization within a single moiré period. Our proposed physics configuration opens an excellent playground for future investigations of strongly correlated flat-band physics as well as the photonic topological phenomena.


[1] Nature 582, 209 (2020), Nano Letters20, 3217 (2020), Nature 577,  42(2020), PRL. 126, 136101 (2021), PRL. 126, 223601, (2021)