We report a Cu $K$- and $L_3$-edge resonant inelastic x-ray scattering study of charge and spin excitations of bulk ${\mathrm{Nd}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$, with a focus on post-growth annealing effects. For the parent compound ${\mathrm{Nd}}_2{\mathrm{CuO}}_4$ $(x=0)$, 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 $R{E}_2{\mathrm{CuO}}_4$ $(\mathrm{RE}=\text{rare earth})$ 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.

中文翻译：

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生长后退火对Nd2-xCexCuO4中电荷和自旋激发的影响

我们报告铜 $ķ$- 和 ${\mathrm{大号}}_3$体电荷和自旋激发的边沿共振非弹性x射线散射研究 ${钕}_{2-X}{策}_X{\mathrm{氧化铜}}_4$，着重于生长后的退火效果。对于母体化合物${钕}_2{\mathrm{氧化铜}}_4$ $（X=0）$，在成长期状态下观察到清晰的电荷转移间隙，而电荷激发光谱表明电子在退火状态下被掺杂。这与退火的薄膜和多晶样品退火的结果一致。$\mathrm{[R}{Ë}_2{\mathrm{氧化铜}}_4$ $（\mathrm{回覆}=\text{稀土}）$在没有Ce掺杂的情况下，Al可以在足够高的电子浓度下变成金属并超导。为了$X=0.16$当Ce浓度降低时，已知氧还原作用会破坏远距离的反铁磁有序并引起超导性，我们发现非超导生长态和超导退火晶体的高能自旋激发几乎相同。这一发现与以前通过中子散射观察到的低能自旋激发的显着变化形成了鲜明的对比。