Scaling Laws for Fluxon Formation in Annular Josephson Tunnel Junctions

It has been argued by Zurek and Kibble that the likelihood of producing defects in a continuous phase transition depends in a characteristic way on the quench rate. In this paper we discuss our experiment for measuring the Zurek-Kibble scaling exponent $\sigma$ for the production of fluxons in annular symmetric Josephson Tunnel Junctions. The predicted exponent is $% \sigma =0.25$,andwefind$\sigma =0.27\pm 0.05$. Further, there is agreement with the ZK prediction for the overall normalisation.