Effects of electron-beam irradiation on the transition properties of YBa₂Cu₃O_7−d grain boundary junctions

Abstract

We have studied the effects of high-energy electron-beam irradiation on the transition properties of superconducting YBa₂Cu₃O_7−d (YBCO) grain boundary junctions, bicrystal junctions and step-edge junctions, on SrTiO₃ substrates. A uniform 1-MeV electron beam irradiated all over the samples. The irradiation doses were 0, 4.7 × 10¹⁴, 4.7 × 10¹⁵, and 4.7 × 10¹⁶ e/cm². For each junction type, we used at least two samples for each dose level and compared the transition parameters before and after irradiation. For comparison, we also studied the same irradiation effects for YBCO microbridges. We measured the resistive transition temperature, the current-voltage characteristics, the normal-state resistance, and the critical current. The effect of irradiation was the most significant for the bicrystal grain-boundary junction and the least significant for the microbridges. The critical current data for the YBCO bicrystal grain-boundary junction showed a maximum at (0.47 ∼ 0.9) × 10¹⁵ e/cm², and those for the microbridges showed a monotonic decrease with increasing dose. The normal-state resistance increased monotonically with increasing dose for all samples by up to ∼40% for the microbridges and ∼20% for the grain-boundary junctions at 4.7 × 10¹⁵ e/cm². The change in the superconducting temperature (T _c) was negligible except for the bicrystal junction at 4.7 × 10¹⁶ e/cm², which was not superconducting at 77 K. These results show that grain-boundary junctions are more susceptive to irradiation, indicating that their critical currents are controllable by using high-energy electron-beam irradiation.