Linearly polarized Cu L3-edge x-ray-absorption near-edge structure of Bi2CaSr2Cu2O8.

Abstract

The linearly polarized Cu ${\mathit{L}}_{3}$-edge x-ray-absorption near-edge structure (XANES) of ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ has been measured and the spectra are interpreted by the full multiple-scattering approach in real space. The polarized spectra over a range of 20 eV can be predicted in terms of the one-electron dipole (\ensuremath{\Delta}l=+1) transition Cu 2p\ensuremath{\rightarrow}\ensuremath{\epsilon}d, probing the unoccupied d-like (l=2) density of states projected on the Cu site with orbital angular momentum ${\mathit{m}}_{\mathit{l}}$=0, 1 in the E?z spectra, and the ${\mathit{m}}_{\mathit{l}}$=2, 1, and 0 in the E\ensuremath{\perp}c spectra. The oscillator strength for the dipole allowed transitions (\ensuremath{\Delta}l=-1) Cu 2p\ensuremath{\rightarrow}\ensuremath{\varepsilon}s is shown to be a factor of 100 weaker than the 2p\ensuremath{\rightarrow}3d transitions. The Coulomb interaction in the final state between the Cu 2p core hole and the excited Cu 3d electron is found to be 5.5 eV forming a bound state below the continuum threshold, the well-known Cu ${\mathit{L}}_{3}$ white line. On the contrary, the core hole induces a nearly rigid redshift about 1 eV of the high-energy conduction bands.