Hard x-ray photoemission study on strain effect in LaNiO${}_3$ thin films

Abstract

The strain effect from a substrate is an important experimental route to control electronic and magnetic properties in transition-metal oxide (TMO) thin films. Using hard x-ray photoemission spectroscopy, we investigate the strain dependence of the valence states in LaNiO${}_3$ thin films, strongly correlated perovskite TMO, grown on four substrates: LaAlO${}_3$, (LaAlO${}_3$)${}_{0.3}$(SrAl${}_{0.5}$Ta${}_{0.5}$O${}_3$)${}_{0.7}$, SrTiO${}_3$, and DyScO${}_3$. A Madelung potential analysis of core-level spectra suggests that the point-charge description is valid for the La ions while it breaks down for Ni and O ions due to a strong covalent bonding between the two. A clear x-ray photon-energy dependence of the valence spectra is analyzed by the density functional theory, which points to a presence of the La 5$p$ state near the Fermi level.

6 pages, 4 figures, and 2 tables

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