Correlation effect in Sr1−xLaxRuO3 studied by soft x-ray photoemission spectroscopy

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.

Interfacial Engineering of Ferromagnetism in Epitaxial Manganite/Ruthenate Superlattices via Interlayer Chemical Doping

“…According to the previous reports on the Sr 1‑ x La x RuO 3 compounds, the La doping can effectively localize the Ru 4d electrons. ,, This is consistent with the La doping-dependent ρ -T curves of the CLRO thin films (Figure S8). As l increases, the ρ increases gradually over the entire T range, and the ρ -T curves clearly display a metal-to-insulator transition at l = 0.67, which indicates that the Ru 4d electrons become highly localized.…”

Avoided quantum criticality and cluster-glass formation in itinerant ferromagnet Sr$_{1-x}$(La$_{0.5}$K$_{0.5}$)$_x$RuO$_3$

“…The development of inhomogeneous FM clusters was also confirmed with µSR measurement [30]. Furthermore, photoemisson experiments revealed that most of the coherent component of Rh 4d electrons remains at the Fermi level in the photoemission spectra for 0.3 ≤ x ≤ 0.5, although the spectral weight transfers from the coherent to incoherent parts with increasing x [31]. It is expected that these anomalous features in Ca-and La-doped SrRuO 3 are intimately coupled with the itinerant-localized duality involved in Ru 4d electrons.…”