Density matrix renormalization group description of the island of inversion isotopes $^{28-33}$F

Abstract

Recent experiments have confirmed that the neutron-rich isotopes $^{28,29}$F belong to the so-called island of inversion (IOI), a region of the nuclear chart around $Z=10$ and $N=20$ where nuclear structure deviates from the standard shell model predictions due to deformation and continuum effects. However, while the general principles leading to the IOI are relatively well understood, the details of the low-lying structure of the exotic fluorine isotopes $^{28-33}$F are basically unknown. In this work, we perform large-scale shell model calculations including continuum states to investigate the properties of the neutron-rich isotopes $^{25-33}$F, using a core of $^{24}$O and an effective two-body interaction with only three adjustable parameters. We adjust the core potential and interaction on experimentally confirmed states in $^{25,26}$O and $^{25-27}$F and solve the many-body problem using the density matrix renormalization group method for open quantum systems in a $sd$-$fp$ model space. We obtain the first detailed spectroscopy of $^{25-33}$F in the continuum and show how the interplay between continuum effects and deformation explains the recent data on $^{28,29}$F, and produces an inversion of the ${5/2}^+$ and ${1/2}^+$ states in $^{29,31,33}$F. Several deformed one- and two-neutron halo states are predicted in $^{29,31}$F, and we predict the ground state of $^{30}$F to have a structure similar to that of the first ${5/2}^+$ state of $^{29}$F. We also suggest several experimental studies to constraint models and test the present predictions. The complex structure of neutron-rich fluorine isotopes offers a trove of information about the formation of the southern shore of the IOI through a subtle interplay of deformation and continuum couplings driven by the occupation of the quasi-degenerate neutron shells $0d_{3/2}$ and $1p_{3/2}$.