Origin of anomalous temperature dependence of Nernst effect in narrow-gap semiconductors

Based on the Boltzmann transport theory, we study the origin of the anomalous temperature dependence of the Nernst coefficient (ν) due to the phonon-drag mechanism. For narrow-gap semiconductors, we find that there are two characteristic temperatures at which a noticeable peak structure appears in ν. Contrarily, the Seebeck coefficient (S) always has only one peak. While the breakdown of the Sondheimer cancellation due to the momentum-dependence of the electron relaxation time is essential for the peak in ν at low T, the contribution of the valence band to the phonon-drag current is essential for the peak at higher T. By considering this mechanism, we successfully reproduce ν and S of FeSb₂ for which a gigantic phonon-drag effect is observed experimentally.

[1] R. Masuki, T. Nomoto, R. Arita. arXiv:2010.11001 (2020)