Search for spontaneous nucleation of magnetic flux during rapid cooling of YBa2Cu3O7-delta films through T-c

We describe an experimental search for spontaneous formation of flux lines during a rapid quench of thin YBa2Cu3O7-delta films through T-c. This effect is expected according to the Kibble-Zurek mechanism of a creation of topological defects of the order parameter during a symmetry-breaking phase transition. Spontaneously formed vortices were previously observed in superfluid He-3, while a similar experiment in superfluid He-4 gave negative results. Using a high-T-c superconducting quantum interference device, we measured both the magnetic flux in the sample during a quench with a sensitivity of 20 phi(0)/cm(2), and the held noise which one would expect from flux lines pinned in the film. The sensitivity was sufficient to detect spontaneous flux ata level corresponding to 10(-3) of the prediction. Within our resolution, we saw no evidence for this effect. [S0163-1929(99)06533-9].