Temperature-activated switchable nonreciprocal thermal emitter via magneto-optical quasi-BIC coupling

Non-Kirchhoff states of thermal radiation, which benefit from their nontrivial nonreciprocal emissivity properties, are crucial for addressing pressing challenges such as global climate change, energy crisis, and overheating of electronic devices. However, significant challenges remain in the quest to develop a design paradigm characterized by nonreciprocal switching to facilitate transformative breakthroughs in non-Kirchhoff radiative devices. Here, we develop a temperature-activated switchable nonreciprocal thermal emitter comprising a silicon cylindrical grating array on InAs/VO₂ films, which enables switchable nonreciprocal thermal radiation for TE modes at λ = 9.481 µm and θ = ±10°, resulting in a remarkable nonreciprocity of 0.45, a high Q-factor of ≈403 for the emissivity, and a switch ratio of 146. Leveraging magneto-optical quasi-bound states in the continuum coupling and VO₂'s phase transition, the structure achieves robust control: (i) a nonreciprocal “on” state with enhanced light-matter interactions in VO₂'s insulating phase, and (ii) a nonreciprocal “off” state with negligible effects in its metallic phase for both TE and TM modes, making it a polarization-selective emitter with switchable nonreciprocal thermal radiation. This work bridges the gap in switchable nonreciprocal thermal radiation research and provides insights into the design of practical nonreciprocal thermal structures, with applications in thermal camouflage, energy conversion, and thermal management.