We report a Cu K- and L3-edge resonant inelastic x-ray scattering study of charge and spin excitations of bulk Nd2−xCexCuO4, with focus on post-growth annealing effects. For the parent compound Nd2CuO4 (x=0), a clear charge-transfer gap is observed in the as-grown state, whereas the charge excitation spectra indicate that electrons are doped in the annealed state. This is consistent with the observation that annealed thin-film and polycrystalline samples of RE2CuO4 (RE = rare earth) can become metallic and superconducting at sufficiently high electron concentrations without Ce doping. For x=0.16, a Ce concentration for which it is known that oxygen reduction destroys long-range antiferromagnetic order and induces superconductivity, we find that the high-energy spin excitations of non-superconducting as-grown and superconducting annealed crystals are nearly identical. This finding is in stark contrast to the significant changes in the low-energy spin excitations previously observed via neutron scattering.
@article{arxiv.2008.03420,
title = {Post-growth annealing effects on charge and spin excitations in Nd$_{2-x}$Ce$_x$CuO$_4$},
author = {Kenji Ishii and Shun Asano and Masumi Ashida and Masaki Fujita and Biqiong Yu and Martin Greven and Jun Okamoto and Di-Jing Huang and Jun'ichiro Mizuki},
journal= {arXiv preprint arXiv:2008.03420},
year = {2021}
}