This paper reports the synthesis and superconducting behaviors of the tetragonal iron-chalcogenide superconductor FeSe. The electrical resistivity and magnetic moment measurements confirmed its superconductivity with a Tcᶻᵉʳᵒ and Tcᵐᵃᵍ at 9.4 K under ambient pressure. EPMA indicated the sample to have a stoichiometric Fe:Se ratio of 1:1 (±0.02). The Seebeck coefficient which was 12.3 μV/K at room temperature, changed to a negative value near 200 K, indicating it to be a two carriers material. Above Tc, the ρ(T) curve revealed an 'S' shape. Hence dρ(T)/dT, and d²ρ(T)/dT² showed pseudogap-like behavior at T^*=110 K according to the resistivity curvature mapping (RCM) method for high Tc cuprates. Moreover, the magnetoresistance ρH(T)/ρH=0 under a magnetic field and the Seebeck coefficient $S(T)$ revealed revealed pseudogap-like behavior near T^*. Interestingly, at the same temperature, 30 K, the sign of $S(T)$ and all signs of d²ρ(T)/dT² changed from negative to positive above Tc.
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Song et al. (2011) studied this question.