Thermoelectricity and electronic correlation enhancement in FeS by light Se doping

We report thermoelectric studies of FeS1-xSex (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 FeS0.94Se0.06 when compared to FeS, which is related not only to Fe but also to chalcogen-derived electronic states.

Automated summary

We report thermoelectric studies on FeS1-xSex superconducting single crystals, which exhibit high irreversibility fields and critical current density comparable to materials with higher superconducting critical temperatures. Substituting selenium in FeS results in significant improvements in Tc/Tf ratio and effective mass, indicating an increase in electronic correlation of the bulk conducting states. First-principle calculations show an increase in the density of states at the Fermi level in FeS0.94Se0.06 compared to FeS, which is related to both iron and chalcogen-derived electronic states.