Nonreciprocal Thermal Fizeau Drag Radiation around Asymmetric Exceptional Points

Magnet-free, far-field infrared nonreciprocal thermal radiation has been reported using Weyl semimetals or spatiotemporal modulation nanostructures, but these methods face challenges like requiring extremely low temperatures or high modulation frequencies and have limited spectral or angular ranges. Here, we demonstrate far-field nonreciprocal thermal Fizeau drag radiation around asymmetric exceptional points (EPs) by drifting electrons in graphene sheets on dielectric periodic nanostructures. First, the generation and evolution mechanisms of symmetric scattering EP pairs have been unveiled in parameter spaces (i.e., w-θ space, w and θ are filling ratio of gratings and incident angle respectively). The EP pairs are connected by bulk Fermi arc along the θ axis whose length can be tuned over the whole angular range by modifying dielectric optical index. Drifting electrons contribute to asymmetrically redistributing EPs with specific angular and spectral positions at low drifting velocities due to Fizeau drag effects. These nonreciprocal behaviors of EPs in angle space have been used to shape magnet-free infrared nonreciprocal emissivity and absorptivity with different numbers of resonant peaks, resulting in more than an order of magnitude increase in wavelength-integrated thermal nonreciprocity. The physics that underpins the synergy between nonreciprocity and EPs offers new insights into areas such as non-Hermitian physics, nonreciprocal optics, and nonreciprocal thermal photonics.