Effects of Ce substitution and and reduction on the electronic states of Nd2-xCexCuO4-y studied by x-ray photoelectron

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

In order to realize superconductivity in cuprates with the T^{'}-type structure, not only chemical substitution (Ce doping) but also postgrowth 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 spectroscopy on superconducting and nonsuperconducting Nd_{2-x}Ce_{x}CuO_{4} (x=0, 0.15, and 0.19) thin films. By postgrowth 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 despite the absence of the Ce substitution.

Ce electronic states in Nd(0.45-x)Ce(x)Sr0.55MnO3 probed by x-ray absorption spectroscopy and photoemission

We have investigated the Ce 4f electronic states in the Ce-doped manganites Nd(0.45-x)Ce(x)Sr0.55MnO3 (NCSMO) by means of x-ray absorption spectroscopy (XAS) and hard x-ray photoelectron spectroscopy (HAXPES). The Ce 3d XAS shows that the Ce ions exist in the form of the Ce(3+) and Ce(4+) mixed-valent states, and we have found that the XAS spectral features change with temperature. The Ce 3d XAS and HAXPES spectra for NCSMO agree reasonably well with calculated results based on the single-impurity Anderson model, which takes into account the atomic multiplets and two valence bands. The estimated Ce bulk valence of Nd0.15Ce0.3Sr0.55MnO3 decreases from 3.44 to 3.30 with cooling.

Crossing the gap from p- to n-type doping: nature of the states near the chemical potential in La(2)-(x)Sr(x)CuO(4) and Nd(2-x)Ce(x)CuO(4-delta)

We report on an x-ray absorption and resonant photoemission study on single crystals of the high-T(c) cuprates La2-xSrxCuO4 and Nd(2-x)Ce(x)CuO(4-delta). Using an intrinsic energy reference, we find that the chemical potential of La2-xSrxCuO4 lies near the top of the La2CuO4 valence band whereas in Nd(2-x)Ce(x)CuO(4-delta) it is situated near the bottom of the Nd2CuO4 conduction band. The data clearly establish that the introduction of Ce in Nd2CuO4 results in electrons being doped into the CuO2 planes. We infer that the states closest to the chemical potential have a Cu 3d(10) singlet origin in Nd(2-x)Ce(x)CuO(4-delta) and a 3d(9)L singlet origin in La2-xSrxCuO4.