Low-temperature thermal conductivity of Co$_{1-x}$M$_x$Si (M=Fe, Ni) alloys

TL;DR

This study investigates the low-temperature electrical and thermal conductivities of CoSi alloys with Fe and Ni, revealing unexpected thermal conductivity enhancement at low temperatures due to phonon scattering mechanisms.

Contribution

It introduces a theoretical model explaining the increased thermal conductivity in CoSi alloys at low temperatures, considering complex electronic structures and disorder effects.

Findings

Electrical conductivity decreases with Fe doping.

Thermal conductivity increases below 20K in alloys.

Model explains phonon scattering by charge carriers.

Abstract

We study the low-temperature electrical and thermal conductivity of CoSi and Co$_{1-x}$M$_x$Si alloys (M = Fe, Ni; $x \leq$ 0.06). Measurements show that the low-temperature electrical conductivity of Co$_{1-x}$Fe$_{x}$Si alloys decreases at $x > $ 0.01 by an order of magnitude compared with that of pure CoSi. It was expected that both the lattice and electronic contributions to thermal conductivity would decrease in the alloys. However, our experimental results revealed that at temperatures below 20K the thermal conductivity of Fe- and Ni-containing alloys is several times larger than that of pure CoSi. We discuss possible mechanisms of the thermal conductivity enhancement. The most probable one is related to the dominant scattering of phonons by charge carriers. We propose a simple theoretical model that takes into account the complex semimetallic electronic structure of CoSi with nonequivalent valleys, and show that it explains well the increase of the lattice thermal conductivity with increasing disorder and the linear temperature dependence of the thermal conductivity in the Co$_{1-x}$Fe$_x$Si alloys below 20K.