Critical properties of the high-energy electron-beam-irradiated superconductor weak links

We have studied the effects of high-energy electron-beam irradiation on the superconducting transition properties of an YBCO bicrystal junction, a focused ion-beam (FIB)-patterned YBCO nanobridge, a MgB2 intergrain nanobridge, and a BaKFeAs multigrain microbridge. We used one sample for each junction type and repeated the irradiation-and-measurement process at 6 accumulated-dose steps: 0, 3 × 1014, 1015, 3 × 1015, 1016, and 1017 e/cm2. A uniform electron beam with a 1-MeV kinetic energy was irradiated indiscrimately over the samples. We measured the resistive transition temperature, the normal-state resistance, and the critical current. The irradiation effect was significant for all the samples except the BaKFeAs microbridge. The critical current data for the YBCO bicrystal junction and the MgB2 intergrain nanobridge had a maximum at 3 × 1015 e/cm2, and the YBCO nanobridge showed a monotonic decrease. For all the samples, the normal state resistance increased monotonically with increasing dose by up to ~20% at 1016 e/cm2, and the change in Tc was negligible. The results showed that the YBCO and MgB2 weak links were susceptive to irradiation, indicating the possibility of controlling the critical current of those junctions by using high-energy electron-beam irradiation.