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The rare-earth nickelates (RNiO$_3$) are a prototypical example of a metal-insulator transition. Among the RNiO$_3$, LaNiO$_3$ is unique in remaining metallic, although highly correlated. Interestingly, superlattices with insulating interlayers of LaAlO$_3$, can be driven insulating and antiferromagnetic if they are thin enough$^{1}$. We have used $^8$Li $\beta$-detected NMR ($\beta$-NMR), to study LaNiO$_3$ as a single crystal, thin film, and in superlattices with LaAlO$_3$. We observe biexponential spin-lattice relaxation which we attribute to electronic phase separation$^{2,3}$. In the single crystal and bulk-like thin film, both phases appear metallic$^{2}$. However, in the ultrathin layers of the superlattices, the behaviour of one of the phases appears magnetic at low temperature$^{3}$.
1. A. V. Boris et al., Science 332, 937 (2011)
2. V. L. Karner et al., Phys. Rev. B 100, 165109 (2019)
3. V. L. Karner et al., Phys. Rev. B. 104, 205114 (2021)
