Pressure Studies for 1111 and 11 Type Iron-based Superconductors

<jats:title>Abstract</jats:title><jats:p>In the recent development of the studies in iron-based superconductors, high-pressure experiments have been played an important role. Large enhancement of Tc with applying pressure and pressure-induced superconductivity were reported in LaFeAsO<jats:sub>1</jats:sub>-<jats:sub>x</jats:sub>F<jats:sub>x</jats:sub>. In this work, electrical, magnetic and structural measurements on 1111 type Ca(Fe<jats:sub>1-x</jats:sub>Co<jats:sub>x</jats:sub>)AsF and 11 type Fe(Se<jats:sub>1-x</jats:sub>Te<jats:sub>x</jats:sub>)<jats:sub>0.92</jats:sub> under high pressure have been performed. For Ca(Fe<jats:sub>1-x</jats:sub>Co<jats:sub>x</jats:sub>)AsF, the substitution of Co suppressed the magnetic and structural transitions and raised superconductivity. Pressure-induced superconductivity was observed for <jats:italic>x</jats:italic> = 0.0 and 0.05. The highest Tc was obtained in parent compound under high pressure, in contrast to LaFeAsO<jats:sub>1-x</jats:sub>F<jats:sub>x</jats:sub>. These results suggest that the substitution of Co increases carrier concentration and induces disorder in the FeAs superconducting layer. For FeTe<jats:sub>0.92</jats:sub>, 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.</jats:p>