Linearly polarized Cu ${\mathit{L}}_3$-edge x-ray-absorption near-edge structure of ${\mathrm{Bi}}_2$${\mathrm{CaSr}}_2$${\mathrm{Cu}}_2$${\mathrm{O}}_8$

The linearly polarized Cu ${\mathit{L}}_3$-edge x-ray-absorption near-edge structure (XANES) of ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{8+\mathrm{\delta }}$ 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 (Δl=+1) transition Cu 2p→εd, 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⊥c spectra. The oscillator strength for the dipole allowed transitions (Δl=-1) Cu 2p→ɛs is shown to be a factor of 100 weaker than the 2p→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.