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 Fe(Se,Te) thin films grown on CaF2. In particular, we carry out a systematic experimental investigation with different irradiation fluences up to 7.30·10 16 cm -2 and different proton implantation depths, in order to clarify whether and to what extent the critical current is enhanced or suppressed, what are the effects of irradiation on the critical temperature, the resistivity and the critical magnetic fields, and finally what is the role played by the substrate in this context.We find that the effect of irradiation on superconducting properties is generally small as compared to the case of other iron-based superconductors. Such effect is more evident on the critical current density Jc, while it is minor on the transition temperature Tc, on the normal state resistivity  and on the upper critical field Hc2 up to the highest fluences explored in this work. In addition, our analysis shows that when protons implant in the substrate far from the superconducting film, the critical current can be enhanced up to 50% of the pristine value at 7 T and 12 K, while there is no appreciable effect on critical temperature and critical fields together with a slight decrease in resistivity. On the contrary, when the implantation layer is closer to the film-substrate interface, both critical current and temperature show a decrease accompanied by an enhancement of the resistivity and the lattice strain. This result evidences that possible modifications induced by irradiation in the substrate may affect the superconducting properties of the film via lattice strain. The robustness of the Fe(Se,Te) system to irradiation induced damage makes it a promising compound for the fabrication of magnets in high-energy accelerators.

Effect of 1.5 MeV Proton Irradiation on Superconductivity in FeSe0.5Te0.5 Thin Films

“…T with respect to the pristine film almost without a decrease in Tc [22]. On the contrary, Jc of 3.5 MeV proton irradiated Fe(Se,Te) films covered with 80 μm thick Al foil decreased by up to 80% after irradiation at 4.2 K. The in-field Jc performance in the irradiated FST films in our study could be attributed to the small number of vortex pinning defects created by the irradiation at low fluence.…”

“…A degradation of T c after the ion irradiation is commonly reported in iron-based superconductors [19], although there have been a few reports on an increased T c in iron-based superconductors irradiated with proton and electron [16,20,21]. In previous work, the Fe(Se,Te) films were covered by Al foil with 80 µm thickness and irradiated with 3.5 MeV protons at doses of 2.68 × 10 16 and 5.35 × 10 16 p/cm 2 , corresponding to 2.30 × 10 -3 and 4.59 × 10 -3 dpa, respectively [22][23][24]. The average bombarding energy of the protons on the Fe(Se,Te) film was calculated to be 1.43 ± 0.07 MeV.…”

“…In contrast, we observed almost no change in the in-field J c above 1 T. Irradiation with MeV protons could produce mostly random point defects and nanocluster [27] due to ion-nucleus collisions. Sylva et al reported that 3.5 MeV proton irradiation with 6.40 × 10 16 p/cm 2 dose (corresponding to 2.27 × 10 -3 dpa) yields J c improvement of about 40% at 4.2 K and 7 T with respect to the pristine film almost without a decrease in T c [22]. On the contrary, J c of 3.5 MeV proton irradiated Fe(Se,Te) films covered with 80 µm thick Al foil decreased by up to 80% after irradiation at 4.2 K. The in-field J c performance in the irradiated FST films in our study could be attributed to the small number of vortex pinning defects created by the irradiation at low fluence.…”

Nanoscale analysis of superconducting Fe(Se,Te) epitaxial thin films and relationship with pinning properties

“…After the milling process, the photoresist was removed by mild sonication in acetone for a few tens of seconds and dried in nitrogen air. Nine Hall bar-shaped micro-bridges 20 μm wide and 50 μm long were realized 29 . The electrical transport properties were investigated by means of a Cryogenic Ltd. full cryogen free cryostat equipped with an integrated cryogen-free variable-temperature insert operating in the range 1.6–300 K up to a maximum magnetic field of 16 T. In this system, the sample was cooled by a continuous helium gas flow and the temperature stability was within 0.01 K. The electrical resistance measurements as a function of the temperature were performed by a four-probe method, and the critical current data were extracted from I-V measurements using the standard voltage criterion set at 10 µV/cm.…”

Effective Magnetic Field Dependence of the Flux Pinning Energy in FeSe0.5Te0.5 Superconductor

“…Several microbridges were patterned by standard UV lithography on 100 nm thick films of Fe(Se,Te). These films have been grown on a CaF 2 substrate by pulsed laser deposition using a Nd:YAG laser at 1024 starting from a target whose nominal composition is FeSe 0.5 Te 0.5 , as previously described [15]. The actual film composition is Fe 0.98 Se 0.67 Te 0.33 and it results in a critical temperature T c = 18.5 K as estimated by the 50% of the normal state resistance criterion.…”