Iron-based superconductors have attracted attention for their elucidation of their superconducting mechanism because they have the simplest crystal structure among iron-based superconductors.On the other hand, in the superconducting transition temperature phase diagram (correlation diagram of temperature and composition that transitions to the superconducting state), there are discontinuous jumps that are not seen in other iron-based superconductors, which is the biggest mystery. Was there.

　In this study, thin films of iron chalcogenide superconductors were prepared on two types of substrates, and the superconducting transition temperature with respect to the amount of tellurium (Te) in the composition was summarized.As a result, the optimum amount of tellurium showing the highest superconducting transition temperature differs depending on the substrate, but discontinuous jumps (sudden ups and downs) appeared in common in the vicinity of the tellurium amount.The research group found that each of these discontinuities is the boundary of the crystal structure change (structural phase transition) of the iron chalcogenide superconductor.

　Iron chalcogenide superconductors exhibit a structural phase transition from tetragonal to orthorhombic below a certain temperature.In this study, it was clarified that the superconducting transition temperature is strongly suppressed in the region where this structural phase transition exists.In other words, it was shown that the structural phase transition and superconductivity are in a competitive relationship, and that the structural phase transition is the origin of the discontinuous jump in the superconducting transition temperature phase diagram.

　This result is expected to have a great influence on the elucidation of the mechanism of iron-based superconductors and iron-based superconductors.

Paper information:[Scientific Reports] Control of structural transition in FeSe1-xTex thin films by changing substrate materials (English)