Evolution of the metallic state of LaNiO$_3$/LaAlO$_3$ superlattices measured by $^8$Li $\beta$-detected NMR

TL;DR

This study uses $^8$Li $eta$-detected NMR to investigate how the metallic state in LaNiO$_3$/LaAlO$_3$ superlattices evolves with layer thickness, revealing two distinct relaxation components with different temperature behaviors.

Contribution

It introduces a novel application of $^8$Li $eta$-detected NMR to probe layer-dependent metallic states in superlattices, uncovering bipartite relaxation phenomena.

Findings

Identification of two relaxation components with different temperature dependencies.

Weak influence of LaNiO$_3$ thickness on the slow component's metallicity.

Strong sensitivity of the fast component to layer thickness and temperature.

Abstract

Using ion-implanted $^8$Li $\beta$-detected NMR, we study the evolution of the correlated metallic state of LaNiO$_3$ in a series of LaNiO$_3$/LaAlO$_3$ 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 LaNiO$_3$ thickness, while the fast component is much more sensitive, exhibiting the opposite temperature dependence (increasing towards low $T$) in the thinnest, most magnetic samples. The origin of this bipartite relaxation is discussed.