Effects of nuclear magnetism on halo phenomena in deformed nuclei

<sec><p indent="0mm">The study of halo phenomenon in exotic nuclei is one of the most fascinating topics in nuclear physics research. In most suggested halo nuclei or candidates from experiments so far, the neutron or proton number is odd. The nonrelativistic or relativistic density functional theory can provide a unified and self-consistent description for atomic nuclei, whether they are even-even, odd-<italic>A</italic> or odd-odd. Within these frameworks, even-even nuclei exhibit time-reversal symmetry, while for odd-<italic>A</italic> and odd-odd nuclei, the unpaired odd nucleon(s) leads to the vector current, which breaks the time-reversal symmetry and results in the time-odd field, also known as, the nuclear magnetism. Existing studies on deeply bound nuclei and rotating nuclei have shown that the nuclear magnetism influences the binding energy, magnetic moment, nuclear rotations, etc. Due to the extremely weak binding properties of halo nuclei, the nuclear magnetism may significantly influence the nuclear stability and halo structure, and the related effects remain to be further explored. </sec><sec> Based on the relativistic density functional theory, the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc), which takes into account the effects of deformation, pairing correlations and continuum simultaneously, has been successfully applied to the descriptions of many halo nuclei, and proved to be a powerful tool to describe both stable and exotic nuclei. It would be interesting to study halo nuclei by combining the DRHBc theory and the nuclear magnetism. </sec><sec> Recently, based on point-coupling density functionals and considering the effects of deformation, pairing correlations, continuum, and nuclear magnetism in a microscopic and self-consistent way, the time-odd deformed relativistic Hartree-Bogoliubov theory in continuum (TODRHBc) was developed, which can provide a unified description for even-even, odd-<italic>A</italic> and odd-odd nuclei with halo structures. By using the TODRHBc theory, a systematic study for the odd-mass and odd-odd nuclei with 8 ≤ <italic>Z</italic> ≤ 20 is performed, and by the comparisons with the results from the DRHBc theory, the effects of nuclear magnetism on ground-state properties are investigated. It is found that the nuclear magnetism always provides additional binding energies, and such additional energies show dependence on nucleon number, deformation and the configuration of single-particle levels. The polarization effect of the nuclear magnetism on the core is discussed. The nuclear magnetism makes odd-mass and odd-odd nuclei impossible to be spherical, and decreases the root-mean-square radii for almost all nuclei, in particular ³¹Ne near the neutron drip line. </sec><sec> By taking the deformed halo nucleus ³¹Ne as an example, the effects of nuclear magnetism in halo nuclei are explored with the TODRHBc theory. A subtle mechanism is revealed that nuclear magnetism may change the single-particle energies and make an unbound nucleus become bound. The distributions of neutron densities and currents are studied in detail. It is shown that ³¹Ne is a one-neutron halo nucleus with a “³⁰Ne+1n” structure, presenting a strong shape decoupling between the prolate one-neutron halo and the near-spherical core. The time-odd currents caused by nuclear magnetism are analyzed in detail, and it is found that in ³¹Ne the halo plays a leading role in the formation of neutron current. </sec>