The effect of energy-dependent electron scattering on thermoelectric transport in novel topological semimetal CoSi

Abstract

Cobalt monosilicide and its solid solutions with Fe or Ni crystallize in B20 cubic noncentrosymmetric structure. These compounds have long been known as promising thermoelectric materials. Recently it was revealed, that they also have unconventional electronic topology. This renewed interest to the investigation of their transport properties. In order to improve theoretical description of thermoelectric transport in these compounds, we take into account electron scattering beyond commonly used constant relaxation time approximation.Using first principle calculations, we investigate the scattering of charge carriers by phonons and point defects. The dependence of the scattering rate on the energy correlates with that for the total density of states. This implies that in this material not only the intraband, but also the interband scattering is important, especially for bands with low density of states. The Seebeck coefficient and the electrical resistivity of CoSi and of dilute solid solutions Co 1−x M x Si (M=Fe or Ni, x < 0.1) are calculated as a function of temperature and the alloy composition. We show that the account of strong energy dependence of relaxation time is important for the description of experimentally observed rapid increase of the resistivity and qualitative change of its temperature dependence with the substitution of cobalt for iron, as well as for the description of the magnitude of the Seebeck coefficient, its temperature and composition dependence.

Band alignment and scattering considerations for enhancing the thermoelectric power factor of complex materials: The case of Co-based half-Heusler alloys

“…Therefore, it is natural to investigate the effect of such a scattering scenario on the TE coefficients under band alignment. In multi-valley multi-band materials the selection rules for each scattering mechanism dictate if the carriers are allowed to scatter only within their current band (intra-band) in the current valley (intra-valley), or whether scattering into states in other bands (inter-band) and other valleys (inter-valley) is also allowed [43][44][45]62 . For intra-band scattering (limited to intra-valley in multi-valley materials), τ IV (E), we have τ i (E) ∝ 1/DOS i (E), and the TD function given by Eq.6 can be simplified to:…”

Electronic Structure of B20 (FeSi-Type) Transition-Metal Monosilicides

“…For example, for stoichiometric CoSi, contribution to the Seebeck coefficient from heavy hole-like bands in constant relaxation time approximation prevail, leading to a positive Seebeck coefficient in contrast to experiment. In CoSi and its solid solutions with a small addition of Ni or Fe, the magnitude of Seebeck coefficient can be quite well described taking into account electron–phonon interactions and point-defect scattering [90]. The energy dependences of these scattering rates, obtained by means of first-principle calculations, appeared to be proportional to the total density of states, implying the importance of interband scattering.…”

Crystal growth and quantum oscillations in the topological chiral semimetal CoSi

“…Tellurium was found to be an appropriate metal flux for the growth of CoSi which yields high-quality single crystals with large magneto-resistance (MR) and carrier mobilities. Although there is plenty of research work on the thermopower of CoSi [16][17][18][19][20][21][28][29][30][31][32], few of them have paid attention to its magneto-Seebeck and Nernst effect.…”