Kondo effect and absence of quantum interference effects in the charge transport of cobalt doped iron pyrite

TL;DR

This study investigates charge transport in cobalt-doped iron pyrite, revealing Fermi liquid behavior, absence of quantum interference effects, and complex magnetic scattering phenomena related to Kondo and spin glass states.

Contribution

It provides the first detailed transport measurements showing the absence of quantum interference effects despite small $k_F\,\ell$, and links magnetic fluctuations to resistivity features in doped iron pyrite.

Findings

Resistivity remains temperature independent below 0.5 K, indicating Fermi liquid behavior.

No quantum corrections to conductivity are observed despite conditions favoring quantum interference.

Resistivity shows Kondo-like behavior for low doping and spin glass characteristics above critical doping.

Abstract

The Hall effect and resistivity of the carrier doped magnetic semiconductor Fe$_{1-x}$Co$_x$S$_2$ were measured for $0\le x \le 0.16$, temperatures between 0.05 and 300 K, and fields of up to 9 T. Our Hall data indicate electron charge carriers with a density of only 10 to 30% of the Co density of our crystals. Despite the previous identification of magnetic Griffiths phase formation in the magnetic and thermodynamic properties of this system for the same range of $x$, we measure a temperature independent resistivity below 0.5 K indicating Fermi liquid-like transport. We also observe no indication of quantum corrections to the conductivity despite the small values of the product of the Fermi wave vector and the mean-free-path, $1.5 \le k_F\ell \le 15$, over the range of $x$ investigated. This implies a large inelastic scattering rate such that the necessary condition for the observation of quantum contributions to the carrier transport, quantum coherence over times much longer than the elastic scattering time, is not met in our samples. Above 0.5 K we observe a temperature and magnetic field dependent resistivity that closely resembles a Kondo anomaly for $x$ less than that required to form a long range magnetic state, $x_c$. For $x>x_c$, the resistivity and magnetoresistance resemble that of a spin glass with a reduction of the resistivity by as much as 35% in 5 T fields. We also observe an enhancement of the residual resistivity ratio by almost a factor of 2 for samples with $x\sim x_c$ indicating temperature dependent scattering mechanisms beyond simple carrier-phonon scattering. We speculate that this enhancement is due to charge carrier scattering from magnetic fluctuations which contribute to the resistivity over a wide temperature range.