Decoupling transition of two coherent vortex arrays within the surface superconductivity state

In magnetic fields applied within the angular range of the surface superconductivity state a magnetically anisotropic layered medium is created in structurally isotropic, sufficiently thick niobium films. Surface (Kulik) vortices residing in the superconducting sheaths on both main film surfaces in tilted fields are shown to undergo a decoupling transition from a coherent to an independent behavior, similar to the behavior observed for Giaever transformer. At the transition a feature in pinning properties is measured, which implies different pinning for the lattice of surface vortices coherently coupled through the normal layer and for two decoupled vortex arrays in the superconducting surface sheaths.