Spontaneous 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 (ZK) scaling exponent sigma for the production of fluxons in annular symmetric Josephson tunnel junctions. The predicted exponent is sigma = 0.25, and we find sigma = 0.27+/-0.05. Further, there is agreement with the ZK prediction for the overall normalization.