In-beam $\gamma$-ray spectroscopy of exotic $N=32$ and 34 nuclei

Recent investigations of exotic $N=32$ and 34 nuclei have highlighted the presence of sizable subshell closures that are absent in stable isotones. The presence of a new subshell closure at $N=34$ was recently reported in $^{54}$Ca, while previous studies focused on the development of the $N=32$ gap in Cr, Ti and Ca. On the theoretical side, these subshells were investigated, for example, in the framework of tensor-force-driven shell evolution, and were attributed to a reordering of the $\nu f_{5/2}$ orbital relative to the $\nu p_{3/2}-\nu p_{1/2}$ spin-orbit partners as protons are removed from the $\pi f_{7/2}$ state. It was also reported that no significant $N=34$ gap exists in Ti isotopes despite the fact that an inversion of $\nu f_{5/2}$ and $\nu p_{1/2}$ has been noted. The strength of the $N=34$ closure in Sc isotopes provides further input on the evolution of the $\nu f_{5/2}$ orbital in exotic systems. Moreover, the structures of Ar isotopes, which are presently reported to $^{48}$Ar, provide information on the magnitude of the $N=32$ closure ``below'' Ca isotopes. In the present work, the low-lying structures of $^{50}$Ar and $^{55}$Sc are reported to investigate further the evolution of the respective $N=32$ and 34 subshell closures in nuclei far from stability.