Linearly polarized CuL3-edge x-ray-absorption near-edge structure ofBi2

Abstract

The linearly polarized Cu L3-edge x-ray-absorption near-edge structure (XANES) of Bi2Sr2CaCu208+z 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 (Al =+1)transition Cu 2p~ed, probing the unoccupied d-like (1=2) density of states projected on the Cu site with orbital angular momentum m& =0, 1 in the E~~z spectra, and the mI=2, 1, and 0 in the Elc spectra. The oscillator strength for the dipole allowed transitions (Al = -1) Cu 2p~v s 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 L3 white line. On the contrary, the core hole induces a nearly rigid redshift about 1 eV of the high-energy conduction bands.

Polarized x-ray absorption spectroscopy study of the symmetry of unoccupied electronic states near the Fermi level in the system

“…This means that there are no unoccupied 3d z 2 orbitals in the system and all 3d unoccupied states must therefore have 3d x 2 −y 2 symmetry alone. This is in agreement with the case of the La-Sr-Cu-O system reported earlier by Chen et al [18] but is in disagreement with the spectra measured earlier in TY mode [6,7,10,11,14,15] which all not only show a 10-20% intensity for the E c case but also report a shift of 300-500 meV for the WL peak towards the lower energy as one goes from E ⊥ c to E c polarization. Suzuki et al [9], on the other hand, do not report observing such a shift in their Cu L 3 spectra measured in TY mode but do report a 5% intensity in the E c polarization.…”

“…Next, the Cu L 3 WLs for E ⊥ c and E c for crystal B are resolved into two Gaussians (figure 3) of FWHM about 1.1 eV separated by about 1.2 eV which is of the order of the charge transfer energy ( ) in the Bi-2212 system. The lower-energy main component L 3 arises from the transition 3d 9 → 2p 3d 10 while the doping-induced satellite component L 3 arises from 3d 9 L → 2p3d 10 L. Given the larger experimental uncertainties, the 3d z 2 -to-3d x 2 −y 2 intensity ratios for the doping-induced satellite peak L 3 are estimated to be 3%. The ratio is thus the same as that for the main peak L 3 .…”

“…High-energy spectroscopy techniques, especially polarized x-ray absorption measurements, have been widely used in probing the electronic states near the Fermi level in these rather complex materials [1,2]. In particular, a number of polarized x-ray absorption spectroscopy (XAS) and electron energy loss spectroscopy (EELS) studies have been made to obtain valuable information on the symmetry of unoccupied states in the normal state [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], and to understand the behaviour of holes in the superconducting state [19,20]. The Bi 2 Sr 2 CaCu 2 O 8 (Bi-2212) compound has attracted more attention because interpretation in the 1-2-3 system is more complicated due to presence of the two non-equivalent Cu sites and because the surfaces of 1-2-3 compounds are unstable at room temperature under UHV conditions.…”

“…More investigations of the Cu L 3 edge [6,7,10,11,14,15] have reported a positive energy shift of about 300-500 meV between the E a, b and E c polarized spectra, but other studies [9,12,16] detect either no shift or a very small relative weight of d z 2 holes with no shift at all. The surface-sensitive total electron yield (TY) mode of detection was used in all the above cases.…”

Fe L-Edge X-ray Absorption Spectroscopy of Low-Spin Heme Relative to Non-heme Fe Complexes: Delocalization of Fe d-Electrons into the Porphyrin Ligand

“…[56][57][58] The spectrum is calculated from the sum of all possible transitions for an electron excited from the 2p level into a 3d level. 67 (D 4h ). Covalent mixing of the metal valence d orbitals with the ligand valence p orbitals is simulated using a charge transfer model which in the case of ligand to metal charge transfer (LMCT) adds a d N+1 L configuration above the d N ground state.…”