The pervasiveness of shape coexistence in nuclear pair condensates

Abstract

We investigate nuclear shape coexistence for a wide range of even-even nuclides. By varying general pair condensates, which include Slater determinants as a limit but also allow for arbitrary pairing channels, we frequently find multiple coexisting mimina, and often more than two. This is consistent with recent experimental results. In order to measure general pairwise correlations beyond a simple Slater determinant, we introduce a novel entropy-like measure, which is smallest mid-shell and largest near shell closures; this is consistent with a picture of pairing-like behavior dominating near closed shells and deformation mid-shell. After surveying nuclides spanning from the $sd$ shell to nuclides between magic numbers 50 and 82, we focus on the six lightest nuclei with shape coexistence. Angular-momentum projected variational pair condensate (PVPC) calculations identify band structures, including two newly proposed coexisting bands in ${}^{26}$Si/Mg and ${}^{24}$Si/Ne. The PVPC results agree well with data, providing robust experimental support for the pervasiveness of coexistence in these light nuclei.

13 pages, 5 figures

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