Anisotropic thermionic response of Weyl semimetals with application in thermionic cooling

摘要

We demonstrate that Weyl semimetals can exhibit intriguing thermionic properties. The emission current varies significantly in systems with different Weyl point separation, the key topological parameter of such materials. The emission is highly anisotropic along directions parallel and perpendicular to the Weyl point separation. For large separations, emission is higher along the perpendicular direction. However, for smaller separations, there exists a changeover temperature at which the dominant emission direction changes from parallel to perpendicular when increasing temperature. The optimal cooling efficiency of a single barrier device can approach 80% of the theoretical limit in the perpendicular direction, 5% greater than a conventional parabolic material. Our results suggest that this class of material has potential applications in thermionic cooling and power generation.