Temporal Evolution of Defects and Related Electric Properties in He-Irradiated YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ Thin Films

TL;DR

This study investigates the stability and effects of He$^+$-ion irradiation-induced defects in YBCO thin films, revealing long-term defect stability, oxygen diffusion characteristics, and enhanced vortex pinning and critical current after years of storage.

Contribution

It provides new insights into the long-term stability of irradiation-induced defects and their impact on superconducting properties in YBCO films, including defect diffusion and vortex pinning enhancements.

Findings

Irradiation-induced defects are stable over nearly six years at room temperature.

Oxygen diffusion has an activation energy of approximately 0.31 eV.

Critical current density increased significantly after long-term storage.

Abstract

Thin films of the superconductor YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) were modified by low-energy light-ion irradiation employing collimated or focused He$^+$ beams, and the long-term stability of irradiation-induced defects was investigated. For films irradiated with collimated beams, the resistance was measured in situ during and after irradiation and analyzed using a phenomenological model. The formation and stability of irradiation-induced defects are highly influenced by temperature. Thermal annealing experiments conducted in an Ar atmosphere at various temperatures demonstrated a decrease in resistivity and allowed us to determine diffusion coefficients and the activation energy $\Delta E = (0.31 \pm 0.03)$ eV for diffusive oxygen rearrangement within the YBCO unit cell basal plane. Additionally, thin YBCO films, nanostructured by focused He$^+$-beam irradiation into vortex pinning arrays, displayed significant commensurability effects in magnetic fields. Despite the strong modulation of defect densities in these pinning arrays, oxygen diffusion during room-temperature annealing over almost six years did not compromise the signatures of vortex matching, which remained precisely at their magnetic fields predicted by the pattern geometry. Moreover, the critical current increased substantially within the entire magnetic field range after long-term storage in dry air. These findings underscore the potential of ion irradiation in tailoring the superconducting properties of thin YBCO films.