Quantum phase transitions and collective enhancement of level density in odd-A and odd-odd nuclei

Abstract

The nuclear shell model assumes an effective mean-field plus interaction Hamiltonian in a specific configuration space. We want to understand how various interaction matrix elements affect the observables, the collectivity in nuclei and the nuclear level density for odd-A and odd-odd nuclei. Using the sd and pf shells, we vary specific groups of matrix elements and study the evolution of energy levels, transition rates and the level density. In all cases studied, a transition between a "normal" and a collective phase is induced, accompanied by an enhancement of the level density in the collective phase. In distinction to neighboring even-even nuclei, the enhancement of the level density is observed already at the transition point. The collective phase is reached when the single-particle transfer matrix elements are dominant in the shell model Hamiltonian, providing a sign of their fundamental role.

28 pages, 8 figures

References in corpus (6)

• Excited state quantum phase transitions in many-body systems
• Quantum phase transitions in the interacting boson model
• Entropy, chaos and excited-state quantum phase transitions in the Dicke model
• Quantum phase transitional patterns in the SD-pair shell model
• Nuclear shape transitions, level density, and underlying interactions
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Cited by in corpus (3)

• Excited-state quantum phase transitions
• From bound states to the continuum
• Level density of the $sd$-nuclei $-$ statistical shell-model predictions