Nd+ isotope shift measurements in a cryogenically cooled neutral plasma

We report measurements of the isotope shifts of two transitions (4f(4)6s -> [25044.7](7/2)(o) and 4f(4)6s -> [25138.6](7/2)(o)) in neodymium ions (Nd+) with hundredfold improved accuracy, using laser spectroscopy of a cryogenically cooled neutral plasma. The isotope shifts were measured across a set of five spin-zero isotopes that spans a nuclear shape transition. We discuss the prospects for further improvements to the accuracy of Nd+ isotope shifts using optical clock transitions, which could enable extremely precise tests of King plot linearity for new physics searches.