Nonreciprocal radiative heat transfer between Weyl semimetal nanoparticles mediated by graphene nanoribbons

We demonstrate tunable thermal rectification enabled by near-field radiative heat transfer between two Weyl semimetal nanoparticles above graphene nanoribbons by rotating the particles and varying their loss factors. We show that, through the rotation, the thermal rectification, quantified by the ratio between the heat powers in the forward and backward directions, is significantly enhanced thanks to the nonreciprocal particles and the substrate that are more strongly coupled than the counterpart systems having reciprocal particles. We reveal that nonreciprocal particles induce spinning Poynting vectors, whose directions can be controlled by rotating the particles and can selectively couple to surface modes excited in the graphene nanoribbons. In addition, by optimizing the loss factor of the particles, the ratio is further improved. Interestingly, we find that when the rotation angles and the loss factor are appropriately chosen, thermal rectification disappears despite nonreciprocal materials in the system. Similarly, the rectification disappears when certain symmetry is satisfied in the system. Our results provide important understanding of nonreciprocal near-field radiative heat transfer in particle-substrate systems involving Weyl semimetals that offer multiple control knobs.