We present a detailed nuclear magnetic resonance (NMR) study of 239Pu in bulk and powdered single-crystal plutonium tetraboride (PuB4), which has recently been investigated as a potential correlated topological insulator. This study constitutes the second-ever observation of the 239Pu NMR signal, and provides unique on-site sensitivity to the rich f-electron physics and insight into the bulk gap-like behavior in PuB4. The 239Pu NMR spectra are consistent with axial symmetry of the shift tensor showing for the first time that 239Pu NMR can be observed in an anisotropic environment and up to room temperature. The temperature dependence of the 239Pu shift, combined with a relatively long spin-lattice relaxation time (T1), indicate that PuB4 adopts a non-magnetic state with gap-like behavior consistent with our density functional theory (DFT) calculations. The temperature dependencies of the NMR Knight shift and T1−1--microscopic quantities sensitive only to bulk states--imply bulk gap-like behavior confirming that PuB4 is a good candidate topological insulator. The large contrast between the 239Pu orbital shifts in the ionic insulator PuO2 (∼~+24.7~\%) and PuB4 (∼~-0.5~\%) provides a new tool to investigate the nature of chemical bonding in plutonium materials.
@article{arxiv.1812.09202,
title = {${}^{239}$Pu nuclear magnetic resonance in the candidate topological insulator PuB$_4$},
author = {A. P. Dioguardi and H. Yasuoka and S. M. Thomas and H. Sakai and S. K. Cary and S. A. Kozimor and T. E. Albrecht-Schmitt and H. C. Choi and J. -X. Zhu and J. D. Thompson and E. D. Bauer and F. Ronning},
journal= {arXiv preprint arXiv:1812.09202},
year = {2019}
}