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Title: Transverse and Longitudinal Magnetothermopower Promoted by Ambipolar Effect in Half-Heusler Topological Materials

Authors: O. Pavlosiuk*, M. Matusiak, A. Ptok, P. Wiśniewski, D. Kaczorowski*

Journal: Advanced Functional Materials

DOI: 10.1002/adfm.202522474

In recent years, half-Heusler phases of the REPtBi and REPdBi families (RE stands for a rare-earth element) have attracted large attention due to their topologically non-trivial electronic structures and the resulting unconventional physical properties. Among these properties are magneto-thermoelectric effects, longitudinal (Seebeck effect) and transverse (Nernst effect), which may be relevant for advancing thermoelectric technologies.

In this article, we present the results of comprehensive studies of the magneto-thermoelectric properties of high-quality single crystals of DyPtBi and DyPdBi, as well as electronic band structure calculations for both materials. The obtained results allowed these materials to be classified as zero-gap semiconductors, in which thermal broadening enables thermal excitation of both electron- and hole-type carriers even at low temperatures. The coexistence of  both carrier types gives rise to an ambipolar effect that strongly influences both magneto-thermopower effects in the studied compounds, with DyPtBi and DyPdBi responding to it in different ways. Our study shows that DyPtBi simultaneously has large longitudinal and transverse magneto-thermopower, defying the conventional trade-off between the two thermoelectric responses typically observed in compensated semimetals. At B = 14 T, Seebeck thermopower of DyPtBi reaches S_xx = 131 μV/K at T =149 K, while its Nernst thermopower attains S_yx = -297 μV/K at T =200 K, one of the largest values reported for topological materials in this temperature range. A comparative analysis with DyPdBi, which shows similarly large S_xx but a much weaker Nernst response, confirms the decisive role of band-structure asymmetry and the degree of carrier compensation in the magnitude of both magneto-thermoelectric responses.

Our results demonstrate that zero-gap semiconductors, exemplified by REPtBi half-Heusler compounds, offer a promising platform for studying magnetic-field-induced enhancements of both transverse and longitudinal thermopower, even near room temperature.