engleski

Vortex pinning and critical currents in nanostructured novel superconductors

Systematic analysis of the parameters associated with vortex pinning in novel superconductors containing nano-scale strong isotropic pinning centres (such as U/n processed Bi2223/Ag tapes and nanoparticle added MgB$_{; ; ; ; 2}; ; ; ; $) has been carried out. Although the systems studied are very different as regards their structures, types of nano-scale defects and vortices, their pinning parameters (irreversibility fields and the fields for the maximum volume pinning force) show distinct common features. In particular, in all these systems the enhancement of the pinning parameters in nanostructured state is, for moderate defect densities $n_{; ; ; ; \phi }; ; ; ; $, approximately linear in $n_{; ; ; ; \phi }; ; ; ; $ over sizable field and temperature windows. Accordingly, these systems exhibit a kind of matching effects with the effective matching field $B_{; ; ; ; \phi }; ; ; ; $, correlated with the areal density of defects. This field $% B_{; ; ; ; \phi }; ; ; ; $ forms a natural field scale for the vortex pinning phenomena in such systems. However, at fields far from $B_{; ; ; ; \phi }; ; ; ; $, an interplay of different pinning mechanisms sets in. The impact of these results for the future enhancement of the flux pinning and critical currents in nanostructured Bi2223 and MgB$_{; ; ; ; 2}; ; ; ; $ superconductors is briefly discussed.

vortex pinning; doping; Bi2223; MgB2

nije evidentirano