Designing Strong and Broadband Nonreciprocal Thermal Radiation in Magnetic Topological Materials

Breaking reciprocity in thermal radiation opens opportunities for energy harvesting, sensing, and thermal management. Traditional nonreciprocal radiative semiconductor devices need an external magnetic field. In this work, we predict a series of magnetic topological materials for magnetic-field-free nonreciprocal thermal radiation in the infrared regime by combining first-principles calculations with Maxwell electrodynamics. We find strong and broadband nonreciprocity in magnetic Weyl semimetals (e.g., Co3Sn2S2), outperforming conventional semiconductor InAs. Furthermore, we propose material design recipes. Strong nonreciprocity requires a large anomalous Hall response relative to the optical loss, whereas the broadband response favors a large optical loss and small dielectric dispersion. Our work establishes a predictive material discovery framework and quantitative design rules for next-generation magnet-free nonreciprocal thermal devices.