Tailoring Fano resonance, optical chirality, and non-Hermitian exceptional points via material-induced symmetry breaking in P-B phase metasurfaces

This study proposes a multiplexed asymmetric metasurface that enables multifunctional terahertz wave manipulation via controlled material-induced symmetry breaking. Unlike conventional geometric asymmetry approaches, the symmetry breaking here stems from tailored material composition variations rather than structural modifications. Remarkably, this symmetry breaking preserves the metasurface's low-frequency response characteristics. It maintains a circular polarization conversion efficiency exceeding 95% and retains the Pancharatnam-Berry phase property within the 0.635–1.525 THz range. Intriguingly, symmetry breaking gives rise to sharp Fano resonances at high frequencies, enabling highly sensitive detection schemes. By carefully engineering material compositions, particularly through the integration of phase-change materials such as VO2, the metasurface demonstrates strong optical chirality. More importantly, leveraging VO2's phase transition allows for dynamic chirality modulation and the controlled emergence of a non-Hermitian exceptional point (EP) in the terahertz spectrum.