X-ray-absorption sum rule for linear dichroism: Application to high-Tc cuprate oxides.

Abstract

Several sum rules for x-ray-absorption (XAS) dichroism have been recently derived. Here we discuss the particular case of linear polarization, relevant to cuprate oxides. We apply this analysis to the ${\mathit{L}}_{2}$ and ${\mathit{L}}_{3}$ edges of ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ in order to obtain quantitative, model-independent information about the out-of-plane character of 3d holes. A Cu 3${\mathit{d}}_{3\mathit{z}}^{2}$-${\mathit{r}}^{2}$ to 3${\mathit{d}}_{\mathit{x}}^{2}$-${\mathit{y}}^{2}$ ratio of 3% is found for an insulating and two superconducting samples, and of 7% for the overdoped one. The interest of measuring both the ${\mathit{L}}_{3}$ and ${\mathit{L}}_{2}$ edges to perform similar XAS sum-rule analysis in higher-${\mathit{T}}_{\mathit{c}}$ cuprates is discussed.