Efficiency and mechanism of heat flux rectification with non-reciprocal surface waves in Weyl-Semi-Metals

We reinvestigate the mechanism of near-field heat-transfer rectification between two Weyl semimetal nanoparticles and a planar Weyl semimetal substrate via the coupling to nonreciprocal surface modes. We first show that the previously predicted rectification ratio of 2673 is incorrect and should rather be 1502 for the same parameters. In addition, we show that the explanation for this enhancement was wrong and must be understood by the coupling to the surface modes in the Weyl semimetal. Furthermore, we provide a detailed study of the enhancement effect as function of different parameters as the distance between the nanoparticles, the Fermi energy, the number of Weyl points, and the temperature. We show that depending on the distance between the nanoparticles there can be a much more efficient heat-flux rectification with ratios of about 6000 than previously predicted. Furthermore, we identify a previously overlooked range of forward rectification and a range of strong backward rectification with rectification ratios larger than 8000 for relatively small Weyl-node separations by using a more precise parameter scan. We investigate the mechanism behind this large heat-flux rectification and study its sensitivity with respect to certain material parameters and temperature showing that even larger rectification ratios up to 15 000 are possible, highlighting that certain Weyl semimetals are strong candidates for highly efficient heat-flux rectification not only for low temperatures but also for room temperatures.