Second-order hyperfine structure and its impact on searches for new physics using isotope-shift spectroscopy
Phys. Rev. A 112, 022804 – Published 5 August, 2025
DOI: https://doi.org/10.1103/qkv8-z8z1
Abstract
Recent precision isotope shift spectroscopy experiments have reported King plot nonlinearities that may uncover previously hidden nuclear properties or hint at new force-carrying bosons. Interpreting the data requires many isotope pairs, but sufficient stable spin-zero nuclei are not always available. In this paper we consider the use of isotopes with nonzero nuclear spin for these studies. We confirm that observed King plot nonlinearity in strontium is explained by a second-order hyperfine shift in the fermionic nucleus, and we discuss the limitations of using Yb isotopes with nonzero spin in King plot studies. By introducing a specific difference of two isotopes with nuclear spin, we allow for a promising addition to future experimental schemes.
