Pressure Studies for 1111 and 11 Type Iron-based Superconductors

In the recent development of the studies in iron-based superconductors, high-pressure experiments have been played an important role. Large enhancement of T c with applying pressure and pressure-induced superconductivity were reported in LaFeAsO 1-x F x . In this work, electrical, magnetic and structural measurements on 1111 type Ca(Fe 1-x Co x )AsF and 11 type Fe(Se 1-x Te x ) 0.92 under high pressure have been performed. For Ca(Fe 1-x Co x )AsF, the substitution of Co suppressed the magnetic and structural transitions and raised superconductivity. Pressure-induced superconductivity was observed for x = 0.0 and 0.05. The highest T c was obtained in parent compound under high pressure, in contrast to LaFeAsO 1-x F x . These results suggest that the substitution of Co increases carrier concentration and induces disorder in the FeAs superconducting layer. For FeTe 0.92 , pressure-induced superconductivity was not detected under high pressure up to 19 GPa, although the resistive anomaly due to the structural and magnetic phase transition was suppressed by applying pressure.