Volume 74, Number 5, June 2006
|Page(s)||817 - 822|
|Section||Electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics|
|Published online||03 May 2006|
Finite-size scaling exponents in the Dicke model
Laboratoire de Physique Théorique de la Matière Condensée, CNRS UMR 7600 Université Pierre et Marie Curie - 4 Place Jussieu, 75252 Paris Cedex 05, France
2 Institut für Theoretische Physik, Universität zu Köln Zülpicher Str. 77, 50937 Köln, Germany
Accepted: 12 April 2006
We consider the finite-size corrections in the Dicke model and determine the scaling exponents at the critical point for several quantities such as the ground-state energy or the gap. Therefore, we use the Holstein-Primakoff representation of the angular momentum and introduce a canonical transformation to diagonalize the Hamiltonian in the normal phase. As already observed in several systems, these corrections turn out to be singular at the transition point and thus lead to nontrivial exponents. We show that for the atomic observables, these exponents are the same as in the Lipkin-Meshkov-Glick model, in agreement with numerical results. We also investigate the behavior of the order parameter related to the radiation mode and show that it is driven by the same scaling variable as the atomic one.
PACS: 42.50.Fx – Cooperative phenomena in quantum optical systems / 05.30.Jp – Boson systems / 73.43.Nq – Quantum phase transitions
© EDP Sciences, 2006
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