Hidden relationship between the electrical conductivity and the Mn 2p core-level photoemission spectra in La_(1-x)Sr_xMnO_3

摘要

Core-level electronic structure of La_(1-x)Sr_xMnO_3 has been studied by x-ray photoemission spectroscopy (XPS). We first report, by the conventional XPS, the well-screened shoulder structure in Mn 2p_(3/2) peak, which had been observed only by hard x-ray photoemission spectroscopy so far. Multiple-peak analysis revealed that the Mn~(4+) spectral weight was not proportional to the nominal hole concentration x, indicating that a simple Mn~(3+)/Mn~(4+) intensity ratio analysis may result in a wrong quantitative elemental analysis. Considerable weight of the shoulder at x = 0.0 and the fact that the shoulder weight was even slightly going down from x = 0.2 to 0.4 were not compatible with the idea that this weight simply represents the metallic behavior. Further analysis found that the whole Mn 2p_(3/2) peak can be decomposed into four portions, the Mn~(4+), the (nominal) Mn~(3+), the shoulder, and the other spectral weight located almost at the Mn~(3+) location. We concluded that this weight represents the well-screened final state at Mn~(4+) sites, whereas the shoulder is known as that of the Mn~(3+) states. We found that the sum of these two spectral weight has an empirical relationship to the conductivity evolution with x.