Correlation effect in Sr$_{1-x}$La$_x$RuO$_3$ studied by soft x-ray photoemission spectroscopy

TL;DR

This study uses soft x-ray photoemission spectroscopy to investigate how La doping affects the electronic structure of Sr$_{1-x}$La$_x$RuO$_3$, revealing increased electron correlation and mixed itinerant-localized electron behavior.

Contribution

It provides the first detailed analysis of La doping effects on electron correlation and the dual nature of Ru 4d electrons in Sr$_{1-x}$La$_x$RuO$_3$ using bulk-sensitive PES.

Findings

Spectral weight transfer from coherent to incoherent states with La doping

Electron correlation effects are intrinsic and bulk-related

Ru 4d electrons exhibit both itinerant and localized characteristics

Abstract

To clarify how the electronic state of Sr1-xLaxRuO3 evolves with La doping, we conducted photoemission (PES) experiments using soft x-rays. The spectral shape of the Ru 4d derived peak near the Fermi level changes significantly with increasing x. This variation indicates that a spectral weight transfer from the coherent to incoherent component occurs due to an enhancement of the electron correlation effect. Resonant PES experiments at the La 3d_{5/2} edge have confirmed that there is no significant contribution of the La 5d state in the energy range where the spectral weight transfer is observed. Using the dependence of the photoelectron mean free path on the photon energy, we subtracted the surface components from the PES spectra and confirmed that the enhancement of the electron correlation effect with La doping is an intrinsic bulk phenomenon. On the other hand, a large portion of the coherent component remains at the Fermi level up to x = 0.5, reflecting that the Ru 4d state still has itinerant characteristics. Moreover, we found that the PES spectra hardly depend on the temperature and do not exhibit a discernible change with magnetic ordering, suggesting that the temperature variation of the exchange splitting does not follow the prediction of the Stoner theory. The presently obtained experimental results indicate that the electron correlation effect plays an important role in Sr1-xLaxRuO3 and that the Ru 4d electrons possess both local and itinerant characteristics.