O1s and Mn2p NEXAFS on single-layered La<Subscript>1-x</Subscript>Sr<Subscript>1+x</Subscript>MnO<Subscript>4</Subscript>: crystal field effect versus orbital coupling mechanism

O1s and Mn2p near-edge X-ray absorption spectroscopy on La<Subscript>1-x</Subscript>Sr<Subscript>1+x</Subscript>MnO<Subscript>4</S ubscript> (0 ≤x ≤0.5) single crystals shows that Sr doping does not only provide holes to the system but also induces a continuous transfer of electrons from out-of-plane d<Subscript>3z2-r2</Subscript> to in-plane d<Subscript>3x2-r2</Subscript>/d<Subscript>3y2-r2</Subscript> orbitals. Furthermore, a non-vanishing electron occupation of in-plane d<Subscript>x2-y2</Subscript> and out-of-plane d<Subscript>3z2-r2</Subscript> orbitals is observed up to relatively high doping contents. These findings demonstrate that the energy difference between all these orbital types has to be very small and manifest that the orbital degree of freedom is determined not just by crystal field effects but also by orbital coupling. Moreover, the doping-dependent transfer of spectral weight observed in the current data identifies La<Subscript>1-x</Subscript>Sr<Subscript>1+x</Subscript>MnO<Subscript>4</S ubscript> as a charge-transfer insulator. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006