London penetration depth of electron-irradiated Ba0.47K0.53Fe2As2

We have characterized an electron-irradiated Ba0.47K0.53Fe2As2 single-crystal using two different techniques: magneto-optic and microwave measurements. The crystal has been measured before as well as after the 2.5 MeV electron irradiation process. After irradiation it was annealed in a number of steps, between 90°C and 180°C. At each step, we employ a resonant microwave cavity technique to determine the London penetration depth changes δλ(ab) and δλ(c) of the sample. Equations based on perturbation theory were derived to calculate δλ(ab) and δλ(c) for a rectangular prism geometry. A procedure to correct the magneto-optic measurements was introduced. We have demonstrated that the superconducting properties of Ba0.47K0.53Fe2As2, degraded by intense electron beam irradiation, can be restored by a simple annealing procedure and the corresponding Uemura plot is in the vicinity of data for hole-doped copper oxides.