Magnetic quadrupole transitions in the relativistic energy density functional theory

TL;DR

This paper investigates magnetic quadrupole (M2) transitions in nuclei using relativistic energy density functional theory, providing insights into their structure, evolution, and experimental limitations, with implications for constraining nuclear magnetic properties.

Contribution

It introduces a relativistic RQRPA approach with an extended residual interaction to study M2 transitions, including their evolution across calcium isotopes and effects of pairing correlations.

Findings

M2 transition strengths are described and compared with experimental data.

Pairing correlations significantly affect M2 strength and energies.

Many experimental strengths are likely missing due to energy range limitations.

Abstract

Background: Magnetic quadrupole (M2) excitation represents a fundamental feature in atomic nucleus associated to nuclear magnetism induced by spin and orbital transition operator. So far it has only been investigated within the non-relativistic theoretical approaches, and available experimental data are rather limited. Purpose: We aim to investigate the properties of M2 transitions in closed and open-shell nuclei using the framework of relativistic nuclear energy density functional. The calculated M2 transition strengths could be used to constrain the quenching of the spin gyromagnetic factors. Methods: The M2 excitations are described using the relativistic quasiparticle random phase approximation (RQRPA) with the residual interaction extended with the isovector-pseudovector term. Results: The M2 transition strength distributions are described and analyzed for closed and open shell nuclei. The results are compared with available experimental data and the strength missing from the experiment is discussed. The evolution of M2 transition properties has been investigated within the $^{36-64} \rm Ca$ isotope chain. Conclusion: The main M2 transitions have rather rich underlying structure and their collectivity increases with the mass number due to larger number of contributing particle-hole configurations. Pairing correlations in open shell nuclei have strong effect, causing the M2 strength reduction and shifting of the centroid energies to higher values. The analysis of M2 transition strengths indicate that considerable amount of experimental strength may be missing, mainly due to limitations to rather restricted energy ranges. The calculated M2 strengths for Ca isotopes, together with the future experimental data will allow constraining the quenching of the $g$ factors in nuclear medium.