Proton-neutron pairing vibrations in N=Z nuclei: Precursory soft mode of isoscalar pairing condensation

Abstract

L=0 proton-neutron ($pn$) pair-addition and pair-removal strengths in ${}^{40}$Ca and ${}^{56}$Ni are investigated by means of the $pn$ particle-particle random-phase approximation employing a Skyrme energy-density functional. It is found that the collectivity of the lowest $J^{\pi }=1^{+}$ state in the adjacent odd-odd nuclei becomes stronger as the strength of the isoscalar (T=0) pairing interaction increases. The results suggest the emergence of the T=0 $pn$-pairing vibrational mode as a possible critical phenomenon toward the T=0 pairing condensation.

Comments: 5 pages including 4 figures. Accepted for publication as a Rapid Communication in Physical Review C