Accelerated vortex dynamics across the magnetic 3D-to-2D crossover in disordered superconductors

Disorder can have remarkably disparate consequences in superconductors, driving superconductor–insulator transitions in ultrathin films by localizing electron pairs and boosting the supercurrent carrying capacity of thick films by localizing vortices (magnetic flux lines). Though the electronic 3D-to-2D crossover at material thicknesses d ~ ξ (coherence length) is well studied, a similarly consequential magnetic crossover at d ~ L c (pinning length) that should drastically alter material properties remains largely underexamined. According to collective pinning theory, vortex segments of length L c bend to adjust to energy wells provided by point defects. Consequently, if d truncates L c , a change from elastic to rigid vortex dynamics should increase the rate of thermally activated vortex motion S . Here, we characterize the dependence of S on sample thickness in Nb and cuprate films. The results for Nb are consistent with collective pinning theory, whereas creep in the cuprate is strongly influenced by sparse large precipitates. We leverage the sensitivity of S to d to determine the generally unknown scale L c , establishing a new route for extracting pinning lengths in heterogeneously disordered materials. Superconductors: Vortices and the role of defects Disorder influences the properties of superconductors, as defects can pin vortices. Thermal energy unpins the vortices, whose creep rate is expected to depend on sample thickness, in particular when the thickness is reduced to below the pinning length. However, the description of pinning in systems with different types of defects is still a matter of debate. Serena Eley at Los Alamos National Laboratory and colleagues systematically studied the thickness dependence of the creep rate of vortices in films of Nb (superconductive critical temperature T c = 9.2 K) and of a cuprate material (T c = 92 K). The results unveil the different role of defects in pinning vortices in these materials and show that this approach provides a means of directly accessing the pinning length in heterogeneously disordered materials, such as cuprates.