Fundamental rule between crystal structure and superconductivity in iron-based superconductors

Abstract

Crystal structures of iron-based superconductors are introduced. Powder neutron diffraction measurements reveal that their crystal structure and superconductivity are strongly correlated. Superconducting transition temperature (T_c) attains a maximum value when FeAs₄ or Fe(Se,Te)₄-Tetrahedrons form a regular shape. Based on this relationship, we have performed high-pressure resistivity experiments on FeSe_0.5Te_0.5, which has the simplest crystal structure in iron-based superconductors. T_c increased rapidly from 14 K to 26 K upon applying pressure up to 2 GPa and we clarified the pressure-induced phase transition from superconducting to metallic phase on the P-T_c phase diagram for the first time.