Fig. 1: The structure of Au-MAPbI₃ metasurface and the properties of BIC.

a Illustration of Au metasurfaces covered with a MAPbI₃ thin film. b The structure of the BIC unit. The geometrical unit cell parameters are: \({P}_{{\rm{x}}}\) = 66 μm, \({P}_{{\rm{y}}}\) = 32 μm, \({L}_{{\rm{x}}}\) = 50 μm, \({L}_{{\rm{y}}}\) = 25 μm, \({L}_{1}\) = 39.5 μm, \(m\) = 5 μm, \(w\) = 5 μm, \(h\) = 200 nm, with the period \(d={P}_{{\rm{x}}}-{L}_{{\rm{x}}}\). The tuning of the resonance position of the BIC modes is realized by introducing multiplicative scaling factor S, which scales the geometrical parameters of metasurfaces by multiplying all parameters by S. Terahertz waves pass through the sample in y-polarization and emerge from the quartz substrate side. (bottom right) Schematic diagram of strong coupling between phonons and BICs. c Quality factor (\(Q\)) of the BIC modes varies with the degree of asymmetry. Red stars represent experimental data, while blue crosses represent the Drude model results, and simulations using parameters employed in the experiment. The orange solid line represents the ideal PEC case. The degree of asymmetry is defined by the expression \(\Delta L=\)L₁-L₂