Pressure tuning of the iron-based superconductor (Ca0.73La0.27)FeAs2

Abstract

Pressure is an efficient tool to tune the electronic structure of iron-based superconductors. Here, we performed systematic high pressure transport and magnetization measurements on (${\mathrm{Ca}}_{0.73}{\mathrm{La}}_{0.27}){\mathrm{FeAs}}_{2}$ single crystal samples. Filamentary superconductivity is induced under a small applied pressure $P=1.6$ GPa. At $P=3.2$ GPa, the superconductivity becomes bulk. It is found that ${T}_{c}$ increases initially and then decreases with further increasing pressure, forming a dome shape. Hall resistivity is measured simultaneously and the Hall coefficient ${R}_{H}$ at 50 K shows nonmonotonic dependence on pressure. In addition, ${R}_{H}$ reverse sign at a critical pressure ${P}_{c}=3.9$ GPa, where ${T}_{c}$ reaches the maximum and there is a sudden increase in superconducting diamagnetism. Theoretical calculation results show a pressure induced Lifshitz transition of the Fermi surface which might be responsible for the appearance of superconductivity.