Chiral near-perfect absorption at exceptional points in non-Hermitian terahertz metasurfaces

This work demonstrates chiral near-perfect absorption at an exceptional point via a loss-asymmetric, non-Hermitian metasurface that synergistically combines chiral exceptional points with a reflective architecture. The meta-atom consists of two orthogonally aligned rectangular resonators. By tailoring the inter-resonator distance, the system is tuned to its exceptional point condition, where the cross-polarized reflection coefficient Rlr for right-circularly-polarized light exhibits a phase singularity, enabling a theoretical absorption maximum of 99.8%. Employing low-loss silver and high-loss titanium nitride as the resonator materials yields a practical absorption of 98% for right-circularly-polarized light and 26% for left-circularly-polarized light. Electric field and power loss density analyses confirm that the chiral absorption dichotomy stems from the asymmetric loss distribution and can be actively controlled by modulating this imbalance. Furthermore, comprehensive parameter sweeps across the metasurface geometry, titanium nitride's collision frequency, and the incident light angle verify the design’s robust tolerance to fabrication imperfections. This study establishes a general framework for designing chiral absorbers and provides a versatile platform for harnessing non-Hermitian physics to manipulate wave polarization and phase.