Fluctuation of mean free path and transition temperature induced vortex pinning in (Ba,K)Fe_2As_2 superconductors

摘要

The vortex pinning mechanisms of Ba_(0.72)K_(0.28)Fe_2As_2 single crystal have been studied systematically as a function of temperature and magnetic field. The temperature dependence of the critical current density, J_C{T), was analysed within the collective pinning model at different magnetic fields. It was found that both the δl pinning mechanism, i.e., pinning associated with charge-carrier mean free path fluctuation, and the δT_C pinning mechanism, which is associated with spatial fluctuations of the transition temperature, coexist in the Ba_(0.72)K_(0.28)Fe_2As_2 single crystal in fields smaller than 4 T. Their contributions are strongly temperature and magnetic field dependent. At lower temperature and B ≤ 4 T, the δl pinning is the dominant mechanism, and its contributions decrease with increasing temperature. At temperatures close to the critical temperature, however, there is evidence for δT_C pinning. At magnetic fields larger than 4 T, the δl pinning mechanism is the only effect.