Description:

Immobilization of flux lines (vortices) is crucial for high-current applications of superconducting materials. Vortex trapping by self-assembled nanoparticles has been established as an efficient route to enhance current-carrying capability of practical superconductors. Pinning mechanisms by such defects are nontrivial. We investigated the problem of a vortex system interacting with an isolated defect using time-dependent Ginzburg-Landau simulations. In the case of a vortex lattice interacting with a large isolated defect, we found a series of first-order phase transitions at well-defined magnetic fields, when the number of vortex lines occupying the inclusion changes. The pin-breaking force has sharp local minima at those fields. As a consequence, in the case of isolated identical large-size defects, the field dependence of the critical current is composed of a series of peaks located in between the occupation-number transition points. We also explored the magnetic-field dependences of critical current for superconductors containing spherical inclusions with different sizes and densities. We found several pinning regimes that indeed are mostly characterized by the average occupation numbers of inclusions with the vortex lines. The distinct peak effect, however, only exists for very small inclusion densities when the vortices form a regular lattice. Our results provide a framework for interpretation of pinning properties of real materials and motivate further generalization of theory.

Dr. Alex Koshelev, Argonne National Lab

Host: John Ketterson

Keywords: Physics, Astronomy, Condensed Matter