Evolution of the metallic state in LaNiO3/LaAlO3 superlattices measured by Li-8 beta-detected NMR

Using ion-implanted Li-8 beta-detected NMR, we study the evolution of the correlated metallic state of LaNiO3 in a series of LaNiO3/LaAlO3 superlattices as a function of bilayer thickness. Spin-lattice relaxation measurements in an applied field of 6.55 T reveal two equal amplitude components: one with metallic (T linear) 1/T-1 and a second with a more complex T dependence. The metallic character of the slow relaxing component is only weakly affected by the LaNiO3 thickness, while the fast component is much more sensitive, exhibiting the opposite temperature dependence (increasing toward low T ) in the thinnest, most magnetic samples. The origin of this bipartite relaxation is discussed in terms of electronic phase separation.