Thermoelectricity and electronic correlations enhancement in FeS by slight 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 $m^{\ast }$ 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.

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