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

Kawasaki, Ikuto*  ; Sakon, Yumi*; Fujimori, Shinichi   ; Yamagami, Hiroshi; Tenya, Kenichi*; Yokoyama, Makoto*

To clarify how the electronic state of Sr$$_{1-x}$$La$$_x$$RuO$$_3$$ evolves with La doping, we conducted photoemission (PES) experiments using soft X rays. The spectral shape of the Ru 4$$d$$-derived peak near the Fermi level changes significantly with increasing $$x$$. This variation indicates that a spectral weight transfer from the coherent to the incoherent component occurs due to an enhancement of the electron correlation effect. Resonant PES experiments at the La 3$$d_{5/2}$$ edge have confirmed that there is no significant contribution of the La 5$$d$$ 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 4$$d$$ 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 Sr$$_{1-x}$$La$$_x$$RuO$$_3$$ and that the Ru 4$$d$$ electrons possess both local and itinerant characteristics.



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Category:Materials Science, Multidisciplinary



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