p x n-Type Transverse Thermoelectrics in a Type-II Weyl Semimetal TaIrTe₄

p x n-type materials refer to materials with a p-type Seebeck coefficient in one direction and a n-type coefficient in the orthogonal direction. This type of materials allows for a transverse thermoelectric response, which is highly desirable for energy applications. Here, we report the observation of p x n-type behavior in TaIrTe₄, a type-II Weyl semimetal, with an in-plane thermopower anisotropy S_xx-S_yy reaching a maximum value 40 μV/K at 200 K. Intriguingly. we found that such a p x n-type behavior is absent in the similar compound NbIrTe₄. The presence and absence of p x n-type behavior in these two materials are consistent with density functional theory calculations, which further predict that the thermopower anisotropy in both compounds can be enhanced up to 130 μV/K by electron doping. Such a strong thermopower anisotropy originates from the presence of both p-type and n-type carriers, each with high mobility in one direction. These results suggest that although type-II Weyl semimetal phase does not guarantee the existence of p x n-type behavior, its unique band structure provides the ingredient to engineer and optimize this phenomenon.