Deformed two-neutron halo in B19

Abstract

Ground state properties of $^{19}\mathrm{B}$ are studied by using the deformed relativistic Hartree-Bogoliubov theory in continuum. The calculations with the density functional PK1 show that $^{19}\mathrm{B}$ is a deformed two-neutron ($2n$) halo nucleus. By examining the evolution of single neutron levels, it is found that the valence levels, which are weakly bound or embedded in the continuum due to pairing, contain considerable $s$-wave components with the probability amplitude of 0.359 and lead to the formation of the halo. Strong quadrupole correlations mix $sd$ orbitals and drive $^{19}\mathrm{B}$ to be prolate. The calculated density of the neutron core presents a prolate shape while the neutron halo is oblate, meaning $^{19}\mathrm{B}$ is a $2n$ halo candidate with shape decoupling effects.