First-Order Quantum Phase Transition in a Finite System
  The dynamics at the critical-point of a general first-order quantum phase transition in a finite system is examined, from an algebraic perspective. Suitable Hamiltonians are constructed whose spectra exhibit coexistence of states corresponding to two degenerate minima in the energy surface separated by an arbitrary barrier. Explicit expressions are derived for wave functions and observables at the critical-point. 
A. Leviatan