Authors: M. Karrer, K. Wurster, J. Linek, M. Meichsner, R. Kleiner, E. Goldobin, and D. Koelle
Phys. Rev. Applied 21, 014065
Abstract: We examined the temporal evolution of Josephson and resistive barriers created by a 30-keV focused helium ion beam in microbridges of epitaxially grown single-crystal YBa2Cu3O7−δ thin films. Repeated electric transport measurements at 4.2 K within 300 days after irradiation revealed an increase in the critical current density jc for devices stored at room temperature under nitrogen atmosphere. This behavior can be described by a diffusion-based model of displaced chain oxygen moving back to original lattice sites, thus healing the barrier and partially restoring critical current. We find that jc ∝ exp(−
√t/τ ) with time t. The relaxation time τ increases exponentially with helium irradiation dose and can exceed several hundred days for high-quality Josephson junctions. To achieve higher diffusion rates and thus shorter relaxation times, we annealed some devices in different oxygen partial pressures, right after irradiation. Within a week, those junctions relaxed to a quasistable state, making this a feasible option to achieve temporal stability of device parameters.
