Alcalde M Aparicio, Bucher M, Emary C, Brandes T
Instituto de Física Teórica, UNESP-São Paulo State University, Caixa Postal 70532-2, 01156-970 São Paulo, SP, Brazil.
Phys Rev E Stat Nonlin Soft Matter Phys. 2012 Jul;86(1 Pt 1):012101. doi: 10.1103/PhysRevE.86.012101. Epub 2012 Jul 18.
We consider the Dicke model in the ultrastrong-coupling limit to investigate thermal phase transitions and their precursors at finite particle numbers N for bosonic and fermionic systems. We derive partition functions with degeneracy factors that account for the number of configurations and derive explicit expressions for the Landau free energy. This allows us to discuss the difference between the original Dicke (fermionic) and the bosonic case. We find a crossover between these two cases that shows up, for example, in the specific heat.
我们考虑在超强耦合极限下的迪克模型，以研究玻色子和费米子系统在有限粒子数(N)时的热相变及其先兆。我们推导了包含简并因子的配分函数，该简并因子考虑了构型的数量，并推导了朗道自由能的显式表达式。这使我们能够讨论原始迪克（费米子）情形和玻色子情形之间的差异。我们发现这两种情形之间存在一个交叉点，例如在比热中就会体现出来。
