Abstract
Plutonium-based correlated electron materials host exotic physical phenomena ranging from unconventional heavy-fermion superconductivity to topological Kondo insulating states. Self-irradiation damage can influence many properties of such radioactive materials. Structural disorder effects due to α radiation have been frequently studied using techniques such as transport, thermodynamics, and x-ray diffraction. Here, we use Pu239 nuclear magnetic resonance (NMR) to study the long-term influence of self-damage on the lattice and local electronic structures in a single crystal of the candidate topological insulator plutonium tetraboride (PuB4). We first characterize the anisotropy of the Pu239 resonance and confirm the local axial-site symmetry inferred from previous polycrystalline measurements. Aging effects are then evaluated over the time frame of six years. We find that, though the static Pu239 NMR spectra show a slight modulation in their shape, their field-rotation pattern reveals no change in Pu239 local site symmetry over time, suggesting that aging has a surprisingly small impact on the spatial distribution of the static hyperfine field. Further, ligand-site B11 NMR finds little time-dependent change in the size of electric field gradient around B11 sites. By contrast, aging has a prominent impact on the Pu239 NMR relaxation processes and signal intensity. Specifically, aging-induced damage manifests itself as an increase in the spin-lattice relaxation time T1, an increased distribution of T1, and a signal intensity that decreases linearly by 20% per year. An effective spin-spin relaxation time T2,eff in the aged sample shortens drastically towards lower temperature, suggesting growth of slow fluctuations of the hyperfine field that are linked to radiation-damage-induced inhomogeneity. Our NMR study sheds light on the interplay of radiation damage and local magnetic interactions in correlated insulators.
| Original language | English |
|---|---|
| Article number | 075152 |
| Journal | Physical Review B |
| Volume | 111 |
| Issue number | 7 |
| DOIs | |
| State | Published - Feb 15 2025 |
Funding
We thank H. Yasuoka, H. E. Mason, A. R. Altenhof, P. F. S. Rosa, and J. D. Thompson for fruitful discussions and comments on aging effects and relaxation rate analyses as well as on the manuscript. The dynamic nuclear spin-lattice relaxation measurements were performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering. The spectral measurements including their rotation and aging studies were supported from the Laboratory Directed Research and Development programs and LANL Office of Experimental Sciences. We additionally thank the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Heavy Element Chemistry program (2020LANLE372) for funding (S.A.K.).