Observation of interacting crossing vortex lattices in Bi₂Sr₂CaCu₂O_8+δ thin films

Scanning Hall probe microscopy and magnetometry have been used to study pancake vortices (PV’s) in highly anisotropic Bi₂Sr₂CaCu₂O_8+δ (BSCCO) thin films. For small perpendicular applied fields we observe well-defined PV stacks which are randomly pinned due to a high density of relatively strong pinning centers in the films. When a strong in-plane magnetic field is added images reveal stripelike flux structures which are quite closely aligned to the in-plane field direction. We conclude that this is a manifestation of Josephson vortex (JV) “decoration” by PV’s, which was recently demonstrated in highly ordered BSCCO single crystals in the crossing lattices regime, allowing independent estimates of the anisotropy parameter to be made. This interpretation is supported by the observation that the presence of an in-plane field suppresses the irreversible magnetization of thicker films. Estimates of the JV-PV crossing force and the PV pinning force are found to be comparable in magnitude and fully consistent with this scenario. We believe that this is the first confirmation of the existence of interacting crossing vortex lattices in strongly pinning BSCCO thin films and could find potential applications in superconducting devices.