Valley-dependent electron-phonon scattering in thermoelectric semimetal Ta${}_2$PdSe${}_6$

Abstract

Quasi-one-dimensional transition-metal chalcogenide Ta${}_2$PdSe${}_6$ is a promising thermoelectric semimetal due to the strong electron-hole asymmetry in the carrier lifetime. However, the microscopic origin of such a strong asymmetry remains unclear. In this study, we theoretically investigate electron-phonon scattering in Ta${}_2$PdSe${}_6$. There is a soft phonon mode mainly consisting of atomic displacements in PdSe${}_4$ chains. This soft mode is strongly coupled with the highest valence band at the $\Gamma$ point, which lies slightly below the Fermi energy, and causes strong electron-phonon scattering. The bottom of the electron pocket energetically overlapped with that band also suffers from strong intervalley scattering, by which the imaginary part of the electron self-energy exhibits a sharp change near the Fermi level. On the other hand, the imaginary part of the self-energy for carriers in the hole pocket shows a moderate energy dependence. Thus, we find that electron-phonon scattering is strongly valley-dependent. Our finding will help us to understand the distinctive transport properties observed in Ta${}_2$PdSe${}_6$.

9 pages, 9 figures

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