Tiedau, J. et al. Laser excitation of the Th-229 nucleus. Phys. Rev. Lett. 132, 182501 (2024).
Elwell, R. et al. Laser excitation of the 229Th nuclear isomeric transition in a solid-state host. Phys. Rev. Lett. 133, 013201 (2024).
Zhang, C. et al. Frequency ratio of the 229mTh nuclear isomeric transition and the 87Sr atomic clock. Nature 633, 63–70 (2024).
Zhang, C. et al. 229ThF4 thin films for solid-state nuclear clocks. Nature 636, 603–608 (2024).
Beeks, K. et al. The thorium-229 low-energy isomer and the nuclear clock. Nat. Rev. Phys. 3, 238–248 (2021).
Beeks, K. et al. Fine-structure constant sensitivity of the Th-229 nuclear clock transition. Nat. Commun. 16, 9147 (2025).
Caputo, A. et al. Sensitivity of nuclear clocks to new physics. Phys. Rev. C 112, L031302 (2025).
Fuchs, E. et al. Searching for dark matter with the 229Th nuclear lineshape from laser spectroscopy. Phys. Rev. X 15, 021055 (2025).
Kazakov, G. A. et al. Performance of a 229Thorium solid-state nuclear clock. New J. Phys. 14, 083019 (2012).
Aeppli, A., Kim, K., Warfield, W., Safronova, M. S. & Ye, J. Clock with 8 × 10−19 systematic uncertainty. Phys. Rev. Lett. 133, 023401 (2024).
Higgins, J. S. et al. Temperature sensitivity of a thorium-229 solid-state nuclear clock. Phys. Rev. Lett. 134, 113801 (2025).
Beeks, K. et al. Growth and characterization of thorium-doped calcium fluoride single crystals. Sci. Rep. 13, 3897 (2023).
Ludlow, A. D., Boyd, M. M., Ye, J., Peik, E. & Schmidt, P. O. Optical atomic clocks. Rev. Mod. Phys. 87, 637–701 (2015).
Marshall, M. C. et al. High-stability single-ion clock with 5.5 × 10−19 systematic uncertainty. Phys. Rev. Lett. 135, 033201 (2025).
Bothwell, T. et al. Resolving the gravitational redshift across a millimetre-scale atomic sample. Nature 602, 420–424 (2022).
Rellergert, W. G. et al. Constraining the evolution of the fundamental constants with a solid-state optical frequency reference based on the Th 229 nucleus. Phys. Rev. Lett. 104, 200802 (2010).
Tkalya, E. V., Varlamov, V. O., Lomonosov, V. V. & Nikulin, S. A. Processes of the nuclear isomer 229mTh (3/2+, 3.5 ± 1.0 eV) resonant excitation by optical photons. Phys. Scr. 53, 296 (1996).
Peik, E. & Tamm, C. Nuclear laser spectroscopy of the 3.5 eV transition in Th-229. Europhys. Lett. 61, 181 (2003).
Peik, E. et al. Nuclear clocks for testing fundamental physics. Quantum Sci. Technol. 6, 034002 (2021).
von der Wense, L. & Seiferle, B. The 229Th isomer: prospects for a nuclear optical clock. Eur. Phys. J. A 56, 277 (2020).
von der Wense, L. et al. Direct detection of the 229Th nuclear clock transition. Nature 533, 47–51 (2016).
Thielking, J. et al. Laser spectroscopic characterization of the nuclear-clock isomer 229mTh. Nature 556, 321–325 (2018).
Seiferle, B. et al. Energy of the 229Th nuclear clock transition. Nature 573, 243–246 (2019).
Masuda, T. et al. X-ray pumping of the 229Th nuclear clock isomer. Nature 573, 238–242 (2019).
Yamaguchi, A. et al. Energy of the 229Th nuclear clock isomer determined by absolute γ-ray energy difference. Phys. Rev. Lett. 123, 222501 (2019).
Sikorsky, T. et al. Measurement of the 229Th isomer energy with a magnetic microcalorimeter. Phys. Rev. Lett. 125, 142503 (2020).
Kraemer, S. et al. Observation of the radiative decay of the 229Th nuclear clock isomer. Nature 617, 706–710 (2023).
Zhang, C. et al. Tunable VUV frequency comb for 229mTh nuclear spectroscopy. Opt. Lett. 47, 5591 (2022).
Elwell, R. et al. Laser-based conversion electron Mössbauer spectroscopy of 229ThO2. Nature 648, 300–305 (2025).
Beeks, K. et al. Optical transmission enhancement of ionic crystals via superionic fluoride transfer: growing VUV-transparent radioactive crystals. Phys. Rev. B 109, 094111 (2024).
Dessovic, P. et al. 229Thorium-doped calcium fluoride for nuclear laser spectroscopy. J. Phys. Condens. Matter 26, 105402 (2014).
Hiraki, T. et al. Controlling 229Th isomeric state population in a VUV transparent crystal. Nat. Commun. 15, 5536 (2024).
Nalikowski, K., Veryazov, V., Beeks, K., Schumm, T. & Krośnicki, M. Embedded cluster approach for accurate electronic structure calculations of 229Th:CaF2. Phys. Rev. B 111, 115103 (2025).
Hiraki, T. et al. Laser Mössbauer spectroscopy of 229Th. Preprint at https://arxiv.org/abs/2509.00041 (2025).
Schaden, F. et al. Laser-induced quenching of the Th-229 nuclear clock isomer in calcium fluoride. Phys. Rev. Res. 7, L022036 (2025).
Mestechkin, M. M. Electric field gradient in cubic and other ionic crystals. J. Phys. Condens. Matter 7, 611–623 (1995).
Dunlap, B. & Kalvius, G. in Handbook on the Physics and Chemistry of the Actinides (eds Freeman, A. J. & Lander, G. H.) Vol. 2, 331–434 (North-Holland, 1985).
Torumba, D., Parlinski, K., Rots, M. & Cottenier, S. Temperature dependence of the electric-field gradient in hcp-Cd from first principles. Phys. Rev. B 74, 144304 (2006).
Haas, H. Temperature dependence of electric-field gradient in Zn and Cd: Replacing the T3/2 law. Phys. Rev. B 109, 064104 (2024).
Shrivastava, K. N. Temperature dependence of the Mössbauer isomer shift. Hyperfine Interact. 26, 817–843 (1985).
Oelker, E. et al. Demonstration of 4.8 × 10−17 stability at 1 s for two independent optical clocks. Nat. Photon. 13, 714–719 (2019).
Milner, W. R. et al. Demonstration of a timescale based on a stable optical carrier. Phys. Rev. Lett. 123, 173201 (2019).
Eshelby, J. D. in Solid State Physics (eds Seitz, F. & Turnbull, D.) Vol. 3, 79–144 (Academic Press, 1956).
Stoneham, A. M. Shapes of inhomogeneously broadened resonance lines in solids. Rev. Mod. Phys. 41, 82–108 (1969).
Pelzl, J., Vargas, H., Dautreppe, D. & Schulz, H. Influence of point defects on the nuclear quadrupole resonance of 35Cl in KClO3 and NaClO3. J. Phys. Chem. Solids 36, 791–796 (1975).
Kanert, O., Kotzur, D. & Mehring, M. Influence of point defects and dislocations on the line shape of nuclear magnetic resonance signals. Phys. Status Solidi B Basic Solid State Phys. 36, 291–300 (1969).
Cohen, M. H. & Reif, F. in Solid State Physics (eds Seitz, F. & Turnbull, D.), Vol. 5, 321–438 (Academic Press, 1957).
Gong, Q. et al. Structures and properties of high-concentration doped Th:CaF2 single crystals for solid-state nuclear clock materials. Inorg. Chem. 63, 3807–3814 (2024).
Beeks, K. The Nuclear Excitation of Thorium-229 in the CaF2 Environment: Development of a Crystalline Nuclear Clock. PhD thesis, Technische Universität Wien, Vienna (2022).
Takatori, S. et al. Characterization of the thorium-229 defect structure in CaF2 crystals. New J. Phys. 27, 043024 (2025).
Pastor, R. C. & Arita, K. Preparation and crystal growth of ThF4. Mater. Res. Bull. 9, 579–583 (1974).
Morgan, H. W. T. et al. A spinless crystal for a high-performance solid-state 229Th nuclear clock. Preprint at https://arxiv.org/abs/2503.11374 (2025).
Reissner, M. in Modern Mössbauer Spectroscopy: New Challenges Based on Cutting-Edge Techniques (eds Yoshida, Y. & Langouche, G.), 381–444 (Springer, 2021).
Liechti, O. & Kind, R. NMR-NQR rotation patterns of single crystals with quadrupolar inhomogeneities. J. Mag. Reson. 85, 480–491 (1989).
Hiraki, T. et al. Experimental apparatus for detection of radiative decay of 229Th isomer from Th-doped CaF2. Hyperfine Interact. 245, 14 (2024).
Terhune, J. E. S. et al. Photoinduced quenching of the 229Th isomer in a solid-state host. Phys. Rev. Res. 7, L022062 (2025).
Guan, M. et al. X-ray-induced quenching of the 229Th clock isomer in CaF2. Preprint at https://arxiv.org/abs/2505.03852 (2025).
Flambaum, V. V. Enhanced effect of temporal variation of the fine structure constant and the strong interaction in 229Th. Phys. Rev. Lett. 97, 092502 (2006).
Jones, R. J., Moll, K. D., Thorpe, M. J. & Ye, J. Phase-coherent frequency combs in the vacuum ultraviolet via high-harmonic generation inside a femtosecond enhancement cavity. Phys. Rev. Lett. 94, 193201 (2005).
Gohle, C. et al. A frequency comb in the extreme ultraviolet. Nature 436, 234–237 (2005).
Matei, D. G. et al. 1.5 μm lasers with sub-10 mHz linewidth. Phys. Rev. Lett. 118, 263202 (2017).
Stellmer, S., Schreitl, M. & Schumm, T. Radioluminescence and photoluminescence of Th:CaF2 crystals. Sci. Rep. 5, 15580 (2015).
Christiansen, J. et al. Temperature dependence of the electric field gradient in noncubic metals. Z. Phys. B Condens. Matter 24, 177–187 (1976).
Brown, R. J. C. Anomalous temperature dependence of NQR frequencies. Z. Naturforsch. A 45, 449–458 (1990).
Shier, J. S. & Taylor, R. D. Temperature-dependent isomer shift and anharmonic binding of Sn 119 in Nb 3 Sn from Mössbauer-effect measurements. Phys. Rev. 174, 346–350 (1968).
Coey, J. M. D., Sawatzky, G. A. & Morrish, A. H. Magnetization and temperature dependence of the Mössbauer spectrum shift for an insulator. Phys. Rev. 184, 334–337 (1969).
Ooi, T. et al. Th-229 nuclear clock frequency record (JILA). Zenodo https://doi.org/10.5281/zenodo.15751158 (2025).

