Realization of the nonreciprocal thermal radiation by the front and back sides of the Weyl semimetal-dielectric multilayer structures

This work proposes the Weyl semimetal-dielectric multilayer structures (WDMSes), both sides of which can realize nonreciprocal thermal radiation. Utilizing the transfer matrix method, the absorptivity αq and emissivity eq are calculated in the mid-infrared wave range. The absorption can be attributed to the defect modes. For both sides of the WDMSes, it is found the nonreciprocity originates as the incident angle is around 15° and a wider incident angle tends to enhance it. By increasing the angle to 45°, the stronger nonreciprocal thermal radiation for the front side is revealed at the wavelength of 4.692 µm and 3.890 µm. In the same way, for the back side, it is displayed at the wavelength of 4.692 µm and 3.896 µm. The relevant factors including the temperature of the Weyl semimetal, the thickness of the dielectric layer unit, the thickness of the defect layer, and the period of the structure are discussed. They can affect the nonreciprocity, as well as shift the absorption and emission bands in the wave and angular range. This work can be applied to heat radiation transfer media, energy conversion devices, thermal storage and emitter, and so on.