Isovector and isoscalar pairing in odd–odd N = Z nuclei within a quartet approach

Negrea, D.; Sandulescu, N.; Gambacurta, D.

doi:10.1093/ptep/ptx071

Cited by 6 publications

(1 citation statement)

References 17 publications

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“…It was further developed in Refs. [8,9,10,11,12,13] to the case of isoscalar pairing and N > Z nuclei. General microscopic quartet models for a shell-model basis with an effective Hamiltonian were also recently proposed [14,15,16,17,18,19].…”

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A quartet BCS-like theory

Baran,

Delion

2019

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We introduce a BCS-like theory for the quartet correlations induced by the isovector pairing interaction. It is based on a coherent state of BCS type and, unlike usual mean field approaches, it displays a vanishing pair anomalous density c † c † = 0. We find good agreement between our theory and the exact results. We discuss how the pairing and quarteting correlations share some similar qualitative features within the BCS approach. However, there is no sharp quarteting phase transition. We also present various ways in which our theory may be further developed.

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confidence: 99%

A quartet BCS-like theory

Baran,

Delion

2019

Preprint

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Disentangling the pair and quartet condensates

2019

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We study the nontrivial interplay of the well known pairing and the more complex quarteting correlations in the particular case of N > Z atomic nuclei. Within the new Analytical Disentangled Condensate model, by implementing the notion of fractional degeneracy we obtain the clear physical picture of a rather weakly interacting mixture of quartet and neutron pair condensates which mainly feel each other's influence through Pauli blocking. The basic idea of our approach may be generalized in order to scrutinize the extent to which similar manifestations are present in various many-body systems.After more than 60 years the pairing correlations, so pervasive in condensed matter, nuclear [1] and particle physics [2], are still actively investigated. In nuclear physics in particular, the richness of many body effects is substantially influenced by presence of two fermion species, protons and neutrons. The existence of four spin-isospin possible combinations allows the formation of strongly correlated four-particle structures, known as quartets, due to the nuclear attractive force. As a result, the α-particle is characterized by a large binding energy. In heavy nuclear systems, this structure survives as an α-cluster, as can be seen from the binding energies. In condensed matter systems, conceptually related manifestations may be identified, for example the formation and condensation of biexcitons in semiconductors [3] or the existence of a quartet superfluid phase in a system of fermionic cold atoms trapped in a one-dimensional optical lattice (see Ref.[4] and references therein). In nuclear systems, α-particles can appear only at relative low nuclear densities [7] on the nuclear surface of α-decaying nuclei [8]. From a theoretical viewpoint, the main difficulty is connected to strong antisymmetrization effects between nucleons entering α-like structures. On the one hand, coordinate space approaches like the THSR ansatz [5] have been successfully applied only to light nuclei or to heavy nucleus+α systems, e.g. 212 Po= 208 Pb+α [6]. On the other hand, configuration space approaches based on correlated quartet structures were recently proven to describe very precisely the four body correlations induced by the residual nuclear interaction [9][10][11][12][13][14][15][16][17][18][19], in both N = Z and N > Z nuclei. A unified microscopic description of real space α clustering and configuration (shell model) space quartet correlations is an open problem in theoretical nuclear physics.Moreover, in N > Z nuclei, it is necessary to consider the interplay of quartet and neutron pair correla- * Email address: virgil.baran@theory.nipne.ro tions. In this work, we aim to provide a clearer physical picture of such systems by developing new theoretical many body methods based on recent advances in the analytical description of pairing and quarteting correlations [20]. We consider N neutrons and Z protons moving outside a self-conjugate inert core which interact through a charge-independent pairing force. The corresponding isovector pa...

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Isovector and isoscalar proton-neutron pairing in N>Z nuclei

et al. 2018

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We propose a particle number conserving formalism for the treatment of isovector-isoscalar pairing in nuclei with N > Z. The ground state of the pairing Hamiltonian is described by a quartet condensate to which is appended a pair condensate formed by the neutrons in excess.The quartets are built by two isovector pairs coupled to the total isospin T = 0 and two collective isoscalar proton-neutron pairs. To probe this ansatz for the ground state we performed calculations for N > Z nuclei with the valence nucleons moving above the cores 16 O, 40 Ca and 100 Sn. The calculations are done with two pairing interactions, one state-independent and the other of zero range, which are supposed to scatter pairs in time-revered orbits. It is proven that the ground state correlation energies calculated within this approach are very close to the exact results provided by the diagonalization of the pairing Hamiltonian. Based on this formalism we have shown that moving away of N=Z line, both the isoscalar and the isovector proton-neutron pairing correlations remain significant and that they cannot be treated accurately by models based on a proton-neutron pair condensate.

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Isovector and isoscalar pairing in odd–odd N = Z nuclei within a quartet approach

Cited by 6 publications

References 17 publications

A quartet BCS-like theory

A quartet BCS-like theory

Disentangling the pair and quartet condensates

Isovector and isoscalar proton-neutron pairing in N>Z nuclei

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