Hidden relationship between the electrical conductivity and the Mn 2p core-level photoemission spectra in La1−xSrxMnO3

Abstract

Core-level electronic structure of La1−xSrxMnO3 has been studied by x-ray photoemission spectroscopy (XPS). We first report, by the conventional XPS, the well-screened shoulder structure in Mn 2p3∕2 peak, which had been observed only by hard x-ray photoemission spectroscopy so far. Multiple-peak analysis revealed that the Mn4+ spectral weight was not proportional to the nominal hole concentration x, indicating that a simple Mn3+/Mn4+ 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 2p3∕2 peak can be decomposed into four portions, the Mn4+, the (nominal) Mn3+, the shoulder, and the other spectral weight located almost at the Mn3+ location. We concluded that this weight represents the well-screened final state at Mn4+ sites, whereas the shoulder is known as that of the Mn3+ states. We found that the sum of these two spectral weight has an empirical relationship to the conductivity evolution with x.

Empirical relationship between x-ray photoemission spectra and electrical conductivity in a colossal magnetoresistive manganite La1−xSrxMnO3

“…This confirms our recent conclusion that this shoulder alone does not represent the metallic conductivity, but the sum of the spectral weight of the both Mn 3+ and Mn 4+ well-screened states does. 12 This fact was not found so far because all previous studies were performed in the lower x-range. Figure 2 shows the valence-band HX-PES and XPS spectra.…”

“…This shoulder is too small to observe in the XPS spectrum of x = 0.8, and can be identified only by multiple-peak fitting. 12 The x-dependence of the electrical conductivity at the room temperature (shown in Fig. 4) is as follows: At x = 0, the system is insulating and shows an insulator-tometal transition at ∼0.2 with increasing x.…”

“…This deviation from the systematics up to x = 0.8 is probably due to a structural phase transition. 12 However, the deviation does not affect the near-E F electronic structure or electrical conductivity because the e g band fades away towards x = 1.0.…”

“…Panel (a) shows that the distinct shoulder at 639-640 eV in Mn 2p 3/2 peak in HX-PES spectra is still observable in XPS spectra of x = 0.0 and 0.4 although the intensity is smaller due to lower bulk sensitivity. 10,12 Panel (b) shows the HX-PES spectra in the Mn 2p 3/2 region. The spectra of x = 0.0 and 0.4 show very good agreement with those of thin films.…”

“…11 However, the full x dependence of the shoulder intensity and its relation to electrical conductivity was not resolved. Recently, Hishida et al 12 found that this shoulder is observable using laboratory x-ray photoemission (XPS) using an Al Kα x-ray source. They investigated the shoulder structure in the full range of x and found that the xdependence of the shoulder intensity did not follow the xdependence of the electrical conductivity.…”