# Nuclear excitations within microscopic EDF approaches : pairing and temperature effects on the dipole response

## TL;DR

This study investigates how nuclear dipole responses in Ni isotopes evolve with neutron number and temperature using microscopic EDF models, revealing new excited states and fragmentation effects due to thermal influences.

## Contribution

It provides a detailed analysis of temperature effects on dipole excitations within a self-consistent QRPA framework based on Skyrme EDFs, including the impact on low-energy strength and pairing correlations.

## Key findings

- Temperature induces new excited states via thermally occupied levels.
- Fragmentation of low-energy strength occurs around neutron separation energies.
- Pairing correlations diminish with increasing temperature, reducing strength below 12 MeV.

## Abstract

In the present work, the isovector dipole responses, both in the resonance region and in the low-energy sector, are investigated using the microscopic nuclear Energy Density Functionals (EDFs). The self-consistent QRPA model based on Skyrme Hartree Fock BCS approach is applied to study the evolution of the isovector dipole strength by increasing neutron number and temperature. First, the isovector dipole strength and excitation energies are investigated for the Ni isotopic chain at zero temperature. The evolution of the low-energy dipole strength is studied as a function of the neutron number. In the second part, the temperature dependence of the isovector dipole excitations is studied using the self-consistent finite temperature QRPA, below and above the critical temperatures. It is shown that new excited states become possible due to the thermally occupied states above the Fermi level, and opening of the new excitations channels. In addition, temperature leads to fragmentation of the low-energy strength around the neutron separation energies, and between 9 and 12 MeV. We find that the cumulative sum of the strength below E$\leq12$ MeV decreases in open-shell nuclei due to the vanishing of the pairing correlations as temperature increases up to T=1 MeV. The analysis of the transition densities in the low-energy region shows that the proton and neutron transition densities display a mixed pattern: both isoscalar and isovector motion of protons and neutrons are obtained inside nuclei, while the neutron transition density is dominant at the surface region.