Evidence for long-range correlations within arrays of spontaneously created magnetic vortices in a Nb thin-film superconductor.

We have imaged spontaneously created arrays of vortices (magnetic flux quanta), generated in a superconducting film quenched through its transition temperature at rates around 10(9) K/s. The spontaneous appearance of vortices is predicted by the Kibble-Zurek and by the Hindmarsh-Rajantie models of phase transitions under nonequilibrium conditions. Differentiating between these models requires a measurement of the internal correlations within the emerging vortex array. In addition to short-range correlations predicted by Kibble and Zurek, we found unexpected long-range correlations which are not described by any of the existing models.

A high resolution magneto-optical system for imaging of individual magnetic flux quanta.

A high-resolution magneto-optical imaging system is described. In this system magneto-optical Kerr effect is utilized for resolving individual flux quanta in a type II superconductor. Using an ultra thin EuSe indicator a spatial resolution of 0.8 microm is achieved.

Design of magneto-optical system for imaging of magnetic flux created during a conductor-superconductor phase transition.

According to the Kibble-Zurek model, flux lines are spontaneously created during a fast conductor-superconductor phase transition. The model predicts both the spatial density and the correlations of the flux array. We present the design of a magneto-optical system with a projected single-flux-line resolution. Such a system can allow detailed measurements of the distribution of flux created spontaneously during a conductor-superconductor phase transition.