Dirac Fermion and Phonon Coupling Toward Giant Nernst Thermoelectric Performance in Topological Semimetal TaSb₂

Electron and hole compensation and ultrahigh mobility of topological semimetals are becoming a guiding principle for designing thermoelectric materials with large Nernst effect, following which several topological semimetals are discovered. Here, beyond the desirable band features, the essential role of Dirac Fermion and phonon coupling is further highlighted for the exceptional Nernst effect. By investigating the topological semimetal of TaSb₂ single-crystalline, a high Nernst thermopower of 1200 µV K^-1 and a giant Nernst power factor (PF_N) of 8300 µW cm^-1 K^-2 are observed, which are record values in the topological XPn₂ (X = Ta, Nb; Pn = As, Sb) family. In particular, the Dirac Fermion and phonon coupling presented by the phonon-drag effect amplifies the respective Seebeck coefficients of electrons and holes and therefore enhances the Nernst thermopower. These results provide new insights for future design of novel materials with large Nernst effects and demonstrate the potential of TaSb₂ for solid-state cooling and thermo-management at cryogenic temperatures.