Quantum Phase Transitions in the Interacting Boson Model: Integrability, level repulsion and level crossing

J. M. Arias, J. Dukelsky, J. E. Garcia-Ramos

Published 2003-09-02Version 1

We study the quantum phase transition mechanisms that arise in the Interacting Boson Model. We show that the second-order nature of the phase transition from U(5) to O(6) may be attributed to quantum integrability, whereas all the first-order phase transitions of the model are due to level repulsion with one singular point of level crossing. We propose a model Hamiltonian with a true first-order phase transition for finite systems due to level crossings.