Doped holes and Mn valence in manganites: a polarized soft x-ray absorption study of LaMnO3 and quasi-2D manganite systems

The question of Mn valence and symmetry and population of doped holes in La1.2Sr1.65Ca0.15Mn2O7 and LaSr2Mn2O7 bilayer single crystals has been studied with polarized soft x-ray absorption spectroscopy. The observed changes in the O K and Mn L spectra with polarization provide a strong indication for the existence of a competition between the charge dynamics and the lattice distortion that leads to transfer of some of the holes doped in the out-of-plane (3z(2)-r(2)) states to the in-plane (x(2)-y(2)) states. The changes observed in these with doping are shown not due to a decrease in the electron population in the d(x2-y2) states but caused by an increase in density of holes in the d(z2-x2) and d(z2-y2) states, and the electrons predominantly occupy the corresponding orthogonal states, i.e., d(3x2-r2) and d(3y2-r2). No evidence is found for the existence of a formal Mn4+ valence state in these systems.