Site-Specific X-Ray Absorption Spectroscopy ofY1−xCaxBa

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

“…It is fair to mention that the lower energy peaks are not purely due to Cu-O chains and Zhang Rice (ZR) singlet, but a contribution of the O 2p hole states in the apical oxygen is also mixed. Previous XAS measurements on Y123 [23,24] showed that this last contribution is extended over the entire valence band energy range (527-529 eV). Therefore it is impossible to distinctly identify the said contribution in the present data obtained on polycrystalline samples.…”

“…This over estimation should be due to the contribution of apical oxygen, that can't be separated in the present data. However, by a comparison with single crystal the XAS measurements of Y123 [24] we can deduce that the apical oxygen signal should be contributing by about 30% to the CH and ZR transitions in our XAS spectra. Therefore, we cannot rule out completely the possibility that Ca substitution could cause a charge transfer between the apical oxygen sites and the CuO 2 planes.…”

“…The region of the XAS spectra between 527-530 eV (the so-called pre-edge region) probes the unoccupied O 2p electronic states near the Fermi level, reached by direct 1s → 2p transition. Therefore, the preedge peak can be used to have direct information on the hole density [23][24][25]. In this energy region, there are two main features (inset of Fig.2): a peak at 528.3 eV due to transitions from O 1s level to the valence band (VB) of mainly O 2p character, and a second peak at 529.3 eV, associated to transitions from O 1s level to upper Hubbard band (UHB), formed by the hybridization of Cu3d 9 and Cu3d 10 L states (where L is a ligand hole).…”

“…Instead, when oxygen doping increases from heavily underdoped y=6.4 (x=0) to optimum doped y=7.13 (x=0), the feature around 932.9 eV gains its weight, while the feature around 934.3 eV disappears. 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].…”

Heterointerface engineered electronic and magnetic phases of NdNiO3 thin films

“…Here we use the experimental values for electrical resistivity in the temperature range corresponding to NFL with temperature scaling T 4/3 to determine what temperature window they predict according to following formulas derived for the three-band model, We numerically calculate equation (27) as shown in Fig. 8.…”