Twist-Controlled Symmetry Breaking in Surface Phonon Polariton Moir\'e Metasurfaces

TL;DR

This study demonstrates how twist-induced moire patterns in surface phonon polariton metasurfaces can control symmetry breaking and mode interactions, enabling directional thermal and infrared photonic functionalities.

Contribution

It introduces a framework for twist-controlled symmetry and mode interaction in polaritonic systems, combining fabrication, experimental characterization, and simulations.

Findings

Twist induces asymmetry in polarization conversion.

Emergent moire periodicities modify mode interactions.

Twist enables directional control of infrared heat transfer.

Abstract

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.