Regular and chaotic classical dynamics in the U(5)-SU(3) quantum phase   transition of the IBM
  We study the classical dynamics in a generic first-order quantum phase transition between the U(5) and SU(3) limits of the interacting boson model. The dynamics is chaotic, of H\'enon-Heiles type, in the spherical phase and is regular, yet sensitive to local degeneracies, in the deformed phase. Both types of dynamics persist in the coexistence region resulting in a divided phase space. 
M. Macek and A. Leviatan
nucl-th nlin.CD quant-ph