Imaging of vortices in 2D superconducting arrays: Magnetic decoration and other methods

Direct observation of vortex configurations has been in the last years an interesting challenge to understanding frustration, coherence and interaction effects in superconducting arrays. Recently, magnetic decoration technique has been used to image vortices in wire arrays. The vortex configuration was found to depend strongly on the frustration. Large domains of commensurate states were observed near low rational frustration. We discuss the observed patterns in terms of the models of ground state vortex configurations in classical arrays. With increasing the width of the wires the frustration effect disappears. We present new results on multiquanta vortices in an array of microholes and an extension of this method to various superconducting arrays. A brief review is given on the recent developments on vortex imaging by other direct methods, mostly scanning probes microscopy, which gives access to dynamical properties of vortices.