The flattening phase transition in systems of trapped ions

Closson, Taunia L. L.; Roussel, Marc R.
October 2009
Canadian Journal of Chemistry;Oct2009, Vol. 87 Issue 10, p1425
Academic Journal
When the anisotropy of a harmonic ion trap is increased, the ions eventually collapse into a two-dimensional structure consisting of concentric shells of ions. This collapse generally behaves like a second-order phase transition. A graph of the critical value of the anisotropy parameter vs. the number of ions displays substructure closely related to the inner-shell configurations of the clusters. The critical exponent for the order parameter of this phase transition (maximum extent in the z direction) was found computationally to have the value � = 1/2. A second critical exponent related to displacements perpendicular to the z axis was found to have the value d = 1. Using these estimates of the critical exponents, we derive an equation that relates the amplitudes of the displacements of the ions parallel to the x�y plane to the amplitudes along the z axis during the flattening process.


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