Superconductors are the only experimentally accessible systems with spontaneously broken gauge symmetries which support topologically nontrivial defects, namely string defects. We propose two experiments whose aim is the observation of the dense network of these strings thought to arise, via the Kibble mechanism, in the course of a spon-taneous symmetry breaking phase transition. We suggest ways to estimate the order of magnitude of the density of flux tubes produced in the phase transition. This may provide an experimental check for the theories of the production of topological defects in a spontaneously broken gauge theory, such as those employed in the context of the early Universe.
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We thank Matthew Fisher for many useful comments and especially for pointing out the difference between the vortex migration and flux tube migration, and Tan-may Vachaspati for pointing out an error in our earlier calculation of net string number through a surface. We are very grateful to Jim Langer, Carl Rosenzweig and Mike Stone for very useful discussions and for comments about flux trapping experiments and the issue of reversibility of intercommuted strings. We also thank Yutaka Hosotani, Fong Liu, Trevor Samols, Sanatan Digal, and Supratim Sengupta for useful discussions. Earlier part of this work was supported by the U.S. Department of Energy under contract number DE-FG02-94ER40823 for S.R. and by the U.S. National Science Foundation under Grant No. PHY89-04035 for A.M.S.