Non‐Hermitian Selective Thermal Emitters using Metal–Semiconductor Hybrid Resonators

All open systems that exchange energy with their environment are non‐Hermitian. Thermal emitters are open systems that can benefit from the rich set of physical phenomena enabled by their non‐Hermitian description. Using phase, symmetry, chirality, and topology, thermal radiation from hot surfaces can be unconventionally engineered to generate light with new states. Such thermal emitters are necessary for a wide variety of applications in sensing and energy conversion. Here, a non‐Hermitian selective thermal emitter is experimentally demonstrated, which exhibits passive PT‐symmetry in thermal emission at 700 °C. Furthermore, the effect of internal phase of the oscillator system on far‐field thermal radiation is experimentally demonstrated. The ability to tune the oscillator phase provides new pathways for both engineering and controlling selective thermal emitters for applications in sensing and energy conversion. Thermal emission arising from a high‐loss plasmonic resonator is coupled to a low‐loss dielectric resonator via a dielectric spacer. As the coupling between the two resonators is varied, an optical phase transition occurs between the PT‐symmetric and broken PT‐symmetry phases. Experimental observations of thermal emission at 700 °C suggest that thermal radiation engineering can benefit from this non‐Hermitian design.