Local Metallic and Structural Properties of the Strongly Correlated Metal LaNiO₃ using ⁸Li β-NMR

We report $\beta$-detected NMR of ion-implanted $^{8}$Li in a single crystal and thin film of the strongly correlated metal LaNiO$_{3}$. In both samples, spin-lattice relaxation measurements reveal two distinct local metallic environments, as is evident from $T$-linear Korringa $1/T_{1}$ below 200 K with slopes comparable to other metals. A small, approximately temperature independent Knight shift of $\sim 74$ ppm is observed, yielding a normalized Korringa product characteristic of substantial antiferromagnetic correlations, but, we find no evidence for a magnetic transition from 4 to 310 K. Two distinct, equally abundant $^{8}$Li sites is inconsistent with the widely accepted rhombohedral structure of LaNiO$_{3}$, but cannot be simply explained by either of the common alternative orthorhombic or monoclinic distortions.