Site-specific and doping-dependent electronic structure ofYBa2Cu3

Abstract

Site-specific and doping-dependent electronic structure of YBa2Cu~O"probed by 0 1s and Cu 2p I-ray-absorption spectroscopy

X-ray absorption spectroscopy of detwinnedPrxY1−

“…11, we emphasize that if the holes were residing in the ZR state, transitions from the O 1s core level into the UHB would exhibit little spectral weight due to the transfer of spectral weight from the UHB to the ZR state. 21,58,60,61 In contrast to this, the spectral weight of the UHB should be observed with the same strength as for oxygen-depleted 6.91 compared to their oxygen-depleted counterparts ͑Figs. 9 and 10͒ and is, therefore, attributed to a generally higher degree of hybridization in this energy range, independent of the Pr concentration.…”

“…In earlier work we assigned the peak at 531.0 eV in the YBa 2 Cu 3 O 6.15 spectrum to transitions into the O͑4͒-Cu͑1͒-O͑4͒ dumbbell of oxygendepleted samples and regarded the intensity of this peak as a measure of vacant O͑1͒ sites. 58 Studying our spectra, it becomes clear that for the Pr-doped sample no distinct peak is observed around 531.0 eV, but instead a broad shoulder. This may be due to contributions from higher-energy hybridizations by which this peak is drowned out.…”

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.…”

“…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].…”