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 Co1-xMxSi (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.