Issue 27, 2025

Design of new thorium nuclear clock materials based on polyatomic ions

Abstract

Compounds of polyatomic anions are investigated theoretically as hosts for thorium in nuclear clock devices. The 229Th nucleus has an excited state at 8.355 eV which can be reached using a VUV laser as demonstrated in recent experiments. Incorporating 229Th into a host crystal is an essential step towards developing an ultra-stable nuclear clock. To be a suitable host, a material must have a band gap larger than the nuclear transition frequency. Thus, most research to date has focused on fluorides like LiSrAlF6 and CaF2, for they feature ionic bonding and large band gaps. Ionicity of chemical bonding can be pushed to its limits by superhalogens – polyatomic anions whose electron affinity can be greater than that of the halogens. An additional concern for fluorides is the presence of 19F nuclear spins in the material that can couple to the spin of the 229Th, detrimental to clock performance. In this work we investigate salts containing superhalogen anions, with the goal of identifying promising new hosts for 229Th clocks. Specifically, we investigate compounds of Ca, Sr, and Ba with three anions – BF4, ClO4, and SO42−. By computing the electronic properties of the pure and thorium-doped materials, we predict that M(BF4)2 have the widest band gaps, making them a promising material class. On the other hand, MSO4 could produce the most accurate clocks by eliminating inhomogeneous broadening due to nuclear spin interactions. These results may guide experimental searches for new 229Th clock materials and offer new opportunities to study this unique nuclear transition in the solid state.

Graphical abstract: Design of new thorium nuclear clock materials based on polyatomic ions

Supplementary files

Article information

Article type
Paper
Submitted
26 Mar 2025
Accepted
16 Jun 2025
First published
17 Jun 2025
This article is Open Access
Creative Commons BY license

Dalton Trans., 2025,54, 10574-10580

Design of new thorium nuclear clock materials based on polyatomic ions

H. W. T. Morgan, H. B. T. Tan, A. Derevianko, R. Elwell, J. E. S. Terhune, E. R. Hudson and A. N. Alexandrova, Dalton Trans., 2025, 54, 10574 DOI: 10.1039/D5DT00736D

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