Critical current density and vortex dynamics in pristine and proton-irradiated Ba0.6K0.4Fe2As2

The screening current density (J) and vortex pinning properties for H parallel to c are studied in optimally hole-doped Ba0.6K0.4Fe2As2 single crystals with a superconducting transition of T-c = 38.6 K. We utilize the irreversible magnetization and its relaxation to evaluate the screening current density and vortex dynamics before and after the introduction of point defects created by 3-MeV proton (H+) irradiation with a dose of 5.8 x 10(16) H+/cm(2). In the as-grown crystal, both J and vortex dynamics are strongly influenced by temperature and magnetic field, indicating that the predominant pinning is not the weak-collective pinning but the strong pinning. With an introduction of point defects, J in the H+-irradiated crystal at 2 K reaches 1.1 x 10(7) A cm(-2), which is one of the largest values in iron-based superconductors. In contrast to the as-grown sample, the sensitivity to the temperature and magnetic field becomes quite mild, and the vortex system is described by a simple weak-collective pinning scenario.