Measurement and Analysis of Normal-State Transport Properties of FeSe Superconductor

Transport properties such as thermal conductivity (κ), Seebeck coefficient (S) and electrical resistivity (ρ) of the FeSe superconductor were measured and analyzed theoretically. The samples were synthesized through a solid-state reaction route via vacuum encapsulation and characterized by X-ray diffraction and Rietveld refinement analysis. It is found that the Seebeck coefficient, S(T), exhibits an anomalous temperature dependence and shows a crossover of sign at around 190 K, which is an artifact of coexistence of electron and hole bands, wherein carrier diffusive Seebeck coefficient S_c^diff(T) and phonon drag contribution S_ph^drag(T) can successfully explain the experimental results. The measured thermal conductivity κ(T) develops a phonon peak at around 80 K, presumably due to various phonon scattering mechanisms. Our thermal conductivity analysis indicates not only phonon thermal conductivity (κ_ph), but also the carrier contribution to thermal conductivity (κ_c) is also important, particularly, around room temperatures. Electrical resistivity of FeSe shows superconducting transition (T_C) around 10 K and shows a metallic temperature dependence above T_C which is explained using the Bloch–Gruneisen function of the temperature-dependent resistivity.