Simple, empirical order parameter for a first order quantum phase transition in atomic nuclei

TL;DR

This paper introduces a simple empirical ratio as an order parameter to identify first order quantum phase transitions in atomic nuclei, validated by data and theoretical models, revealing degeneracies and symmetries near criticality.

Contribution

It proposes a new, easy-to-measure empirical signature for first order phase transitions in nuclei, linking experimental data with theoretical IBA model predictions.

Findings

The ratio of 6+ to 0+ energies effectively signals phase transition order.

Data in Nd-Dy regions support the ratio's effectiveness.

Degeneracies in energy levels suggest underlying symmetries at criticality.

Abstract

A simple, empirical signature of a first order phase transition in atomic nuclei is presented, the ratio of the energy of the 6+ level of the ground state band to the energy of the first excited 0+ state. This ratio provides an effective order parameter which is not only easy to measure, but also distinguishes between first and second order phase transitions and takes on a special value in the critical region. Data in the Nd-Dy region show these characteristics. In addition, a repeating degeneracy between alternate yrast states and successive excited 0+ states is found to correspond closely to the line of a first order phase transition in the framework of the Interacting Boson Approximation (IBA) model in the large N limit, pointing to a possible underlying symmetry in the critical region.