Semi-Classical Approach to the Two-Level Pairing Model --Various Aspects   of Phase Change--
  Aspects of the phase change of the two-level pairing model are investigated in the semi-classical treatment by using the variational approch with the mixed-mode coherent state. In the classical limit, $hbar \to 0$, the sharp phase transition appears and the two phases exist in the region where the force strength is larger than a certain critical value. However, it is shown that, in the semi-classical treatment, the above-mentioned behavior of the phase change disappears in the analytical and the numerical treatments. As a result, new understanding about aspects of the phase change in this model is given. 
Y.Tsue (Kochi Univ., Japan), C.Providencia (Univ. de Coimbra,   Portugal), J. da Providencia (Univ. de Coimbra, Portugal) an...