Modulation of transport properties of MgB2 thin films via X-ray irradiation and nanopatterning

High-quality MgB2 thin films were patterned into microbridges and exposed to synchrotron nanoprobe irradiation under varying incidence angles and dwell times. Pristine superconducting microbridges exhibited sharp transitions and relatively low room-temperature resistivity rho pri. Post-irradiation, most bridges became non-superconducting and displayed a dramatic increase in their resistivity rho irr, linked to oxygen incorporation. They also developed a disordered metallic phase and their transition width increased by about two orders of magnitude. At the lowest value of the resistivity ratio rho irr/rho pri, current-voltage characteristics at 10 K revealed abrupt voltage jumps with hysteresis, consistent with SNS Josephson coupling or phase-slip-lines mechanisms. The characteristic voltage aligned with focused-ion-beam-fabricated arrays of sixty MgB2-based Josephson junctions, suggesting sigma-band features for the supercurrent. These results demonstrate synchrotron nanoprobes as precise tools for nanoscale defect engineering and phase control in MgB2, and suggest pathways for tuning its superconducting properties, with possible future applications in quantum technologies.