Symmetry breaking phase transitions play an important role in nature. When a system traverses such a transition at a finite rate, its causally disconnected regions choose the new broken symmetry state independently. Where such local choices are incompatible, topological defects can form. The Kibble-Zurek mechanism predicts the defect densities to follow a power law that scales with the rate of the transition. Owing to its ubiquitous nature, this theory finds application in a wide field of systems ranging from cosmology to condensed matter. Here we present the successful creation of defects in ion Coulomb crystals by a controlled quench of the confining potential, and observe an enhanced power law scaling in accordance with numerical simulations and recent predictions. This simple system with well-defined critical exponents opens up ways to investigate the physics of non-equilibrium dynamics from the classical to the quantum regime.
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We thank B. Damski and R. Rivers for suggestions and comments on the manuscript, L. Yi for his contributions to the detection software, E. Passemar for providing statistics codes and K. Thirumalai for assistance in the lab. This work was supported by NSF PHY11-25915, the United States Department of Energy through the LANL/LDRD Program and a LANL J. Robert Oppenheimer fellowship (A.d.C.), the EU STREP PICC, the Alexander von Humboldt Foundation (M.B.P.), Career Integration Grant (CIG) no. 321798 (A.R.), by EPSRC (R.N.) and by DFG through QUEST. A.d.C. and W.H.Z. are grateful to KITP for hospitality.