Anomalous thermal radiation due to the chiral magnetic effect in Weyl semimetals

Thermal radiation, universally governed by Planck's law for objects at nonzero temperatures, is known to deviate in the near-field regime. In the present paper, we uncover a distinctive thermal radiation behavior in Weyl semimetals, challenging the established principles of Planck's law, even in the far-field regime. The chiral anomaly inherent to these materials gives rise to unique electromagnetic phenomena---namely, the anomalous Hall effect, which cause a breakdown of Kirchhoff's law, and the chiral magnetic effect. We theoretically demonstrate that the latter effect can induce negative emissivity at low-frequency ranges, suggesting an energy transfer from cooler to warmer bodies. This unexpected emissivity opens up novel approaches for thermal energy management using Weyl semimetals, with significant potential for future technological innovations.