Electron energy-loss and x-ray absorption spectroscopy of cuprate superconductors and related compounds

The distribution of the doped holes in La2−xSrxCu1−yRuyO4−δ

“…5) at the energy of the main peak of La 2 Li 0:5 Cu 0:5 O 4 . Such a weak shoulder has also observed previously in La 2Àx Sr x CuO 4 [12,14,27], where the holes in CuO 2 plane created by Sr doping have mainly O 2p and only little Cu 3d character. This is a result of the fact that to achieve a 3d 8 10 L final state in Cu L 2;3 XAS.…”

“…Sample B(1.76, 0.8, 0) is one exception with a 0.5 eV shift to lower energy. We attribute this larger shift to strong excitonic effects [12], which is a reasonable supposition considering the narrow linewidth for this oxide. The single peak in CuO is assigned to a 2p 3d 10 final state arising from the 3d 9 initial state of Cu(II).…”

“…Therefore, O K XAS spectra are usually studied in order to explore unoccupied states with O 2p character above E F induced by covalence in the ground state, or by doping-induced hole occupancy of the O 2p states. The O K XAS spectra of La 2Àx Sr x CuO 4 had been intensively studied previously both experimentally and theoretically in polarization-dependent measurements [12,14,15]. In Fig.…”

“…Spectroscopic studies using X-ray absorption (XAS) at the Cu L 3;2 and O K edges are well known to be standard methods for studying Cu valence and the hybridization between Cu 3d and O 2p states in cuprates [12][13][14][15][16][17]. In addition, our previous combined theoretical and experimental work on model Ru(IV) and Ru(V) oxides indicated that the Ru L 2;3 XAS spectra -as concerns both their energy position and spectral profileare sensitive to the valence state of Ru [18].…”

Soft x-ray absorption and high-resolution powder x-ray diffraction study of superconducting Ca La1−Ba1.75−La0.25+Cu3O system

“…The shoulder at ~932.9 eV is associated to Cu 3d 9 L → Cu 2p3d 10 L transitions and its spectral weight is proportional to the hole number in the valence band [23,24,[30][31][32][33]. The peak at ~934.3 eV is present only in the spectra of the heavily underdoped samples (y=6.4, x=0 and y=6.4, x=0.3) and is ascribed to Cu 1+ states in the O(4)-Cu(1)-O(4) dumbbell [23][24][25][26]. The total holes, obtained from the Cu L 3 XAS line shape analysis are also included in TABLE 1, together with the site-specific holes obtained from the O K-edge analysis.…”