Channeling of Magnetic Flux in YBa2Cu3O7-x Superlattices

Abstract

We report an unusual effect of channeled magnetic flux motion in YBa2Cu3O7−δ/PrBa2Cu3O7−δ superlattices grown by pulsed laser deposition. Magneto-optical imaging reveals that flux moves along a set of parallel and perpendicular lines, while optical microscopy does not show any features on the surface that may cause this effect. In contrast, scanning electron microscopy registers sub-micron fractures in the superlattices, corresponding to the flux lines, but the magnetic flux channels are much wider than the width of these fractures. To further clarify the origin of flux channels, electrical transport measurements on the superlattices have been performed. Their current-voltage characteristics reveal the 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 least resistive way. The application of very large current overheated the superlattice along these channels evaporating superconducting material and exposing wider than in the superconductor fractures 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−δ/PrBa2Cu3O7−δ, but also stresses developed in the superconducting material appearing due to the fracturing of the substrate.