Thermoelectricity and electronic correlations enhancement in FeS by slight Se substitution

TL;DR

This study investigates how slight Se substitution in FeS enhances thermoelectric properties and electronic correlations, evidenced by increased $T_c$/$T_F$, effective mass, and density of states, supported by experimental and first-principle calculations.

Contribution

It demonstrates that minor Se doping in FeS significantly boosts electronic correlations and thermoelectric performance, a novel insight into tuning superconducting properties.

Findings

Se substitution increases $T_c$/$T_F$ and effective mass.

Density of states at Fermi level rises with Se doping.

Electronic correlations are enhanced by Se substitution.

Abstract

We report thermoelectric studies of FeS$_{1-x}$Se$_x$ ($x$ = 0, 0.06) superconducting single crystals that feature high irreversibility fields and critical current density $J_c$ comparable to materials with much higher superconducting critical temperatures ($T_c$'s). The ratio of $T_c$ to the Fermi temperature $T_F$ is very small indicating weak electronic correlations. With a slight selenium substitution on sulfur site in FeS both $T_c$/$T_F$ and the effective mass $m^*$ rise considerably, implying increase in electronic correlation of the bulk conducting states. The first-principle calculations show rise of the density of states at the Fermi level in FeS$_{0.94}$Se$_{0.06}$ when compared to FeS which is related not only to Fe but also to chalcogen-derived electronic states.