Impact of Two-Body Currents on Magnetic Dipole Moments of Nuclei

We investigate the effects of two-body currents on magnetic dipole moments of medium-mass and heavy nuclei using the valence-space in-medium similarity renormalization group with chiral effective field theory interactions and currents. Focusing on near doubly magic nuclei from oxygen to bismuth, we have found that the leading two-body currents globally improve the agreement with experimental magnetic moments. Moreover, our results show the importance of multishell effects for <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mmultiscripts><a:mrow><a:mi>Ca</a:mi></a:mrow><a:mprescripts/><a:none/><a:mrow><a:mn>41</a:mn></a:mrow></a:mmultiscripts></a:mrow></a:math>, which suggest that the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>Z</c:mi><c:mo>=</c:mo><c:mi>N</c:mi><c:mo>=</c:mo><c:mn>20</c:mn></c:math> gap in <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:mmultiscripts><e:mrow><e:mi>Ca</e:mi></e:mrow><e:mprescripts/><e:none/><e:mrow><e:mn>40</e:mn></e:mrow></e:mmultiscripts></e:mrow></e:math> is not as robust as in <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mrow><g:mmultiscripts><g:mrow><g:mi>Ca</g:mi></g:mrow><g:mprescripts/><g:none/><g:mrow><g:mn>48</g:mn></g:mrow></g:mmultiscripts></g:mrow></g:math>. The increasing contribution of two-body currents in heavier systems is explained by the operator structure of the center-of-mass dependent Sachs term.