Observation of the near-threshold intruder 0– resonance in 12Be

A resonant state at $3.21^{+0.12}_{–0.04}$ MeV, located just above the one-neutron separation threshold, was observed for the first time in 12Be from the 11Be(d,p)12Be one-neutron transfer reaction in inverse kinematics. This state is assigned a spin-parity of 0– according to the systematics of the level scheme of the N=8 isotones and decay-width analysis. Gamow coupled-channel and Gamow shell-model calculations show the importance of the continuum coupling, which dramatically influences the excitation energy and ordering of low-lying states. Various exotic structures associated with cross-shell intruding configurations in 12Be and in its isotonic nucleus 11Li are comparably discussed.