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

Abstract

In order to realize superconductivity in cuprates with the T'-type structure, not only chemical substitution (Ce doping) but also post-growth reduction annealing is necessary. In the case of thin films, however, well-designed reduction annealing alone without Ce doping can induce superconductivity in the T'-type cuprates. In order to unveil the origin of superconductivity in the Ce-undoped T'-type cuprates, we have performed bulk-sensitive hard x-ray photoemission and soft x-ray absorption spectroscopies on superconducting and non-superconducting Nd${}_{2-x}$Ce${}_x$CuO${}_4$ ($x=$ 0, 0.15, and 0.19) thin films. By post-growth annealing, core-level spectra exhibited dramatic changes, which we attributed to the enhancement of core-hole screening in the CuO${}_2$ plane and the shift of chemical potential along with changes in the band filling. The result suggests that the superconducting Nd${}_2$CuO${}_4$ film is doped with electrons and that the electronic states are similar to those of Ce-doped superconductors.

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• Angle-resolved photoemission spectroscopy of the low-energy electronic structure of superconducting Pr${}_2$CuO${}_4$ driven by oxygen non-stoichiometry
• Extended superconducting dome of electron-doped cuprates after protect annealing revealed by ARPES
• 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
• Superconductivity induced by structural reorganization in the electron-doped cuprate Nd${}_{2-x}$Ce${}_x$CuO${}_4$
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• Muon spin relaxation study of the spin correlation in the overdoped regime of electron-doped high-Tc cuprate superconductors
• Nature of carrier doping in T'-La1.8-xEu0.2SrxCuO4 studied by X-Ray Photoemission and Absorption Spectroscopy
• Tunable superconductivity in parent cuprate Pr${}_2$CuO${}_{4\pm \delta }$ thin films
• Orbital-selective metal skin induced by alkali-metal-dosing Mott-insulating Ca${}_2$RuO${}_4$
• Distinct variation of electronic states due to annealing in La${}_{1.8}$Eu${}_{0.2}$CuO${}_4$ and Nd${}_2$CuO${}_4$
• Inhomogeneous reduction-annealing effects on the electron-doped cuprate superconductor revealed by micro-focused angle-resolved photoemission spectroscopy
• Cu-spin Correlation in the Electron-overdoped High-Tc Cuprate Thin Films of La_2-x_Ce_x_CuO_4_ Probed by Low-energy Muons