Flux Channeling in YBa2Cu3O7Superlattices

Abstract

We report unusual effect of channeled magnetic flux flow in YBa2Cu3O7-PrBa2Cu3O7- superlattices grown by pulsed laser deposition. Magneto-optical imaging reveals that flux moves along a set of mutually perpendicular lines, while optical microscopy does not show any features on the surface that may cause this effect. In contrast, scanning electron microscopy registers corresponding to the flux lines, sub-micron fractures in the superlattices, but magnetic flux channels are much wider than width of these fractures. To further clarify origin of flux channels, electrical transport measurements on the superlattices have been performed. Their current-voltage characteristics reveal presence of distinctive branches related to the flux motion along the selective channels, following which magnetic flux can cross the sample in a shortest and less resistive way. The application of very large current overheated superlattice along these channels evaporating superconducting material and exposing wider than in superconductor cracks in the substrate. It is concluded that motion of flux in the channels is controlled not only by the presence of nano-fractures in YBa2Cu3O7- PrBa2Cu3O7-, but also stresses developed in superconducting material appearing due to fracturing of substrate.