Distinct variation of electronic states due to annealing in La${}_{1.8}$Eu${}_{0.2}$CuO${}_4$ and Nd${}_2$CuO${}_4$

Abstract

We performed Cu {\it K}-edge X-ray absorption fine structure measurements on T'-type La${}_{1.8}$Eu${}_{0.2}$CuO${}_4$ (LECO) and Nd${}_2$CuO${}_4$ (NCO) to investigate the variation in the electronic state associated with the emergence of superconductivity due to annealing. The X-ray absorption near-edge structure spectra of as-sintered (AS) LECO are quite similar to those of AS NCO, indicating that the ground state of AS T'-type LECO is a Mott insulator. We found a significant variation of the electronic state at the Cu sites in LECO due to annealing. The electron density after annealing ($n_{\mathrm{AN}}$) was evaluated for both superconducting LECO and non-superconducting NCO and found to be 0.40 and 0.05 electrons per Cu, respectively. In LECO but not in NCO, extended X-ray absorption fine structure analysis revealed a softening in the strength of the Cu-O bond in the CuO${}_2$ plane due to annealing, which is consistent with the screening effect on phonons in the metallic state. Since the amounts of oxygen loss due to annealing ($\delta$) for LECO and NCO are comparable with each other, these results suggest distinct electron-doping processes in the two compounds. That electron-doping in NCO approximately follows the relation $n_{\mathrm{AN}}=2\delta$ can be understood if electrons are doped through oxygen deficiency, but the anneal-induced metallic nature and large $n_{\mathrm{AN}}$ of LECO suggest a variation of the electronic band structure causes self-doping of carriers. The origin of the difference in doping processes due to annealing is discussed in connection with the size of the charge transfer gap.

arXiv comment6 pages, 4 figures, 1 table

References in corpus (19)

• Spin correlations in the electron-doped high-transition-temperature superconductor Nd{2-x}Ce{x}CuO{4+/-delta}
• Strength of Correlations in electron and hole doped cuprates
• Mott Transitions and d-wave Superconductivity in Half-Filled-Band Hubbard Model on Square Lattice with Geometric Frustration
• Apical oxygens and correlation strength in electron and hole doped copper oxides
• Magnetic and superconducting phase diagram of electron-doped Pr${}_{1-x}$LaCe${}_x$CuO${}_4$
• Suppression of the antiferromagnetic pseudogap in the electron-doped high-temperature superconductor by "protect annealing"
• Anomalous Dispersion of Longitudinal Optical Phonons in $\mathbf{N}{\mathbf{d}}_{1.86}\mathbf{C}{\mathbf{e}}_{0.14}\mathbf{Cu}{\mathbf{O}}_{4+\mathbf{\delta }}$ Determined by Inelastic X-ray Scattering
• Superconductivity phase diagrams of electron doped cuprates R(2-x)CexCuO4 (R = La, Pr, Nd, Sm, and Eu)
• Evolution of the electronic state through the reduction annealing in electron-doped Pr_1.3-x_La_0.7_Ce_x_CuO_4+delta_ (x=0.10) single crystals: Antiferromagnetism, Kondo effect and superconductivity
• Generic phase diagram of "electron-doped" T' cuprates
• Dispersion of the high-energy phonon modes in Nd${}_{1.85}$Ce${}_{0.15}$CuO${}_4$
• Strong electron correlation behind the superconductivity in Ce-free and Ce-underdoped high-Tc T'-cuprates
• Electronic inhomogeneity and competing phases in electron-doped superconducting Pr0.88LaCe0.12CuO4
• New superconduting cuprates with no effective doping: T'-(La3+)2-x(RE3+)xCuO4
• Electronic Structure of Ce-Doped and -Undoped Nd${}_2$CuO${}_4$ Superconducting Thin Films Studied by Hard X-ray Photoemission and Soft X-ray Absorption Spectroscopy
• Angle-resolved photoemission spectroscopy of the low-energy electronic structure of superconducting Pr${}_2$CuO${}_4$ driven by oxygen non-stoichiometry
• Ce-doping and reduction annealing effects on electronic states in Pr${}_{2-x}$Ce${}_x$CuO${}_4$ studied by Cu $K$-edge X-ray absorption spectroscopy
• Post-growth annealing effects on charge and spin excitations in Nd${}_{2-x}$Ce${}_x$CuO${}_4$
• Successive magnetic ordering sequence observed from muon spin rotation in T'-structured R2CuO4 (R = Eu, Nd)