Moiré-driven electromagnetic responses and magic angles in a sandwiched hyperbolic metasurface

Recent moiré configurations provide a new platform for tunable and sensitive photonic responses, as their enhanced light–matter interactions originate from the relative displacement or rotation angle in a stacking bilayer or multilayer periodic array. However, previous findings are mostly focused on atomically thin condensed matter, with limitations on the fabrication of multilayer structures and the control of rotation angles. Structured microwave moiré configurations are still difficult to realize. Here, we design a novel moiré structure, which presents unprecedented capability in the manipulation of light–matter interactions. Based on the effective medium theory and S-parameter retrieval process, the rotation matrix is introduced into the dispersion relation to analyze the underlying physical mechanism, where the permittivity tensor transforms from a diagonal matrix to a fully populated one, whereas the permeability tensor evolves from a unit matrix to a diagonal one and finally becomes fully filled, so that the electromagnetic responses change drastically as a result of stacking and rotation. Besides, the experiment and simulation results reveal hybridization of eigenmodes, drastic manipulation of surface states, and magic angle properties by controlling the mutual rotation angles between two isolated layers. Here, not only a more precisely controllable bilayer hyperbolic metasurface is introduced to moiré physics, the findings also open up a new avenue to realize flat bands at arbitrary frequencies, which shows great potential in active engineering of surface waves and designing multifunctional plasmonic devices.