Effects of high-energy proton irradiation on the superconducting properties of Fe(Se,Te) thin films

Abstract

In this paper we explore the effects of 3.5 MeV proton irradiation on\nFe(Se,Te) thin films grown on CaF2. In particular, we carry out a systematic\nexperimental investigation with different irradiation fluences up to 7.30x10^16\ncm^-2 and different proton implantation depths, in order to clarify whether and\nto what extent the critical current is enhanced or suppressed, what are the\neffects of irradiation on the critical temperature, the resistivity and the\ncritical magnetic fields, and finally what is the role played by the substrate\nin this context. We find that the effect of irradiation on superconducting\nproperties is generally small as compared to the case of other iron-based\nsuperconductors. Such effect is more evident on the critical current density\nJc, while it is minor on the transition temperature Tc, on the normal state\nresistivity and on the upper critical field Hc2 up to the highest fluences\nexplored in this work. In addition, our analysis shows that when protons\nimplant in the substrate far from the superconducting film, the critical\ncurrent can be enhanced up to 50% of the pristine value at 7 T and 12 K, while\nthere is no appreciable effect on critical temperature and critical fields\ntogether with a slight decrease in resistivity. On the contrary, when the\nimplantation layer is closer to the film-substrate interface, both critical\ncurrent and temperature show a decrease accompanied by an enhancement of the\nresistivity and the lattice strain. This result evidences that possible\nmodifications induced by irradiation in the substrate may affect the\nsuperconducting properties of the film via lattice strain. The robustness of\nthe Fe(Se,Te) system to irradiation induced damage makes it a promising\ncompound for the fabrication of magnets in high-energy accelerators.\n