Madelung potentials and covalency effect in strained La$_{1-x}$Sr$_x$MnO$_3$ thin films studied by core-level photoemission spectroscopy

TL;DR

This study examines core-level shifts in strained La$_{0.6}$Sr$_{0.4}$MnO$_3$ thin films, revealing ionic behavior at La and Sr sites and covalent effects at oxygen and manganese sites through photoemission spectroscopy.

Contribution

It provides experimental evidence of covalency effects in strained manganite thin films by comparing core-level shifts with theoretical Madelung potential calculations.

Findings

La and Sr core-level shifts match calculations, indicating ionic character.

O and Mn core-level shifts are negligible, showing covalent bonding effects.

Strain influences electronic structure and covalency in the films.

Abstract

We have investigated the shifts of the core-level photoemission spectra of La$_{0.6}$Sr$_{0.4}$MnO$_3$ thin films grown on three kinds of substrates, SrTiO$_3$, (LaAlO$_3$)$_{0.3}$-(SrAl$_{0.5}$Ta$_{0.5}$O$_3$)$_{0.7}$, and LaAlO$_3$. The experimental shifts of the La 4d and Sr 3d core levels are almost the same as the calculation, which we attribute to the absence of covalency effects on the Madelung potentials at these atomic sites due to the nearly ionic character of these atoms. On the other hand, the experimental shifts of the O $1s$ and Mn $2p$ core levels are negligibly small, in disagreement with the calculation. We consider that this is due to the strong covalent character of the Mn-O bonds.