Parity inversion, breakdown of shell closure and particle-vibration coupling in Be-isotopes

Abstract

The coupling of single-particle motion and of vibrations in ${}_4^{11}$Be produces dressed neutrons which spend only a fraction of the time in pure single-particle states, and which weighting differently from the bare neutrons, lead to parity inversion. The interaction of the two least bound neutrons in the ground state of ${}_4^{12}$Be mediated by the $v_{14}$ Argonne nucleon-nucleon potential and by the exchange of the phonon cloud, give rise to a strongly correlated state, where the neutrons spend more than half of the time in (s${}^2$+d${}^2$)-configurations, resulting in a breaking of the N=8 shell closure.