On Critical Current Enhancement in Dislocated, Deoxygenated and Irradiated Superconductors: A Unified Approach

As is well-known [1], the technological usage of any superconducting materials is based on their ability to carry (without loss) significant critical currents in strong enough applied magnetic fields. This ability is directly related to pinning efficiency of a given material which in turn is determined by its crystallographic structure and the presence of different kinds of defects (both inherent and introduced artificially). In conventional superconductors, the magnetic flux flowing through the crystal is assumed to be pinned by practically immobile (frozen) pinning centers (except perhaps for a possibility of thermal fluctuations around their equilibrium positions). In high-Tc superconductors (HTS) the situation is much more complicated because of the smallness of their coherence length and, as a result, of practically inevitable formation of intricate weak-link structure even within a single grain (the so-called intragranular granularity [2]). Hence, any defects (imperfections) in these materials will contribute not only to their flux pinning ability but will also determine their weak-link properties. Such dualism brings about a lot of interesting anomalies in HTS (for the recent reviews on the subject, see, e.g., [3, 4] and further references therein) and calls for non-traditional pinning scenarios capable of explaining the observed non-trivial electronic transport behavior in these materials. In the present paper, one of the possible scenarios is proposed based on a novel concept of vortex pinning via defect-induced intragrain weak links which takes advantage of the abovementioned dualism of (extended) defects (as pinning centers and weak links) in HTS by allowing pinning centers to participate in the pinning process more actively. By considering a subtle balance between different forces acting upon an extended (dislocations) and point (oxygen vacancies) defects to stabilize their