Twist-Controlled Symmetry Breaking in Surface Phonon Polariton Moiré Metasurfaces
Moire lattices provide a powerful route for engineering emergent symmetries and length scales through the relative rotation of periodic structures. However, their implementation in polaritonic systems remains relatively unexplored, and a general framework describing how twist modifies the interaction of optical modes in momentum space is still lacking. Here, we investigate how twist-induced moire periodicities can control symmetry and momentum-space coupling in surface phonon polariton (SPhP) metasurfaces. We fabricate twisted overlapping dual-grating metasurfaces on a polar dielectric substrate with dielectric overlayer and characterize their optical response using polarization-resolved Fourier-transform infrared microscopy. Experimental measurements are combined with full-wave simulations and momentum-space analysis to identify the resonant SPhP and SPhP-like waveguide (WG) modes arising from both individual grating periodicities and emergent moire periodicities. The results reveal twist-controlled symmetry breaking manifested as asymmetry between p to s and s to p polarization conversion, along with twist-dependent interactions between SPhP and SPhP-like WG modes. Our analysis reveals that the twist-engineered polarization-conversion asymmetry enables directional biasing of infrared radiative heat transfer. These findings establish twisted phonon-polaritonic metasurfaces as a versatile platform for geometry-controlled symmetry engineering in the mid-infrared. Future work may leverage such twist-programmable polaritonic interactions to enable directional thermal emission, polarization-selective detection, and reconfigurable infrared photonic devices.