Electron-doped cuprates require not only electron doping by chemical substitution but also post-growth reduction annealing for realizing superconductivity. However, electron concentration can also be varied by reduction annealing, making it challenging to disentangle the respective influences of electron concentration and oxygen non-stoichiometry. Here, by combining alkali-metal dosing and angle-resolved photoemission spectroscopy, we monitored changes in the electronic structure of an electron-doped cuprate while supplying additional electrons to its surface without modifying oxygen content. Whereas a Fermi surface reconstruction due to long-range antiferromagnetic order was suppressed by alkali-metal deposition, the pseudogap -- which is associated with short-range spin/charge correlations and can be suppressed by efficient reduction annealing -- was found to persist. The results highlight significant contribution of impurity oxygen atoms to pseudogap formation in electron-doped cuprates.
@article{arxiv.2604.25450,
title = {Differentiation of electron doping and oxygen reduction in electron-doped cuprates},
author = {M. Miyamoto and M. Horio and K. Moriya and A. Takahashi and K. Tanaka and Y. Koike and T. Adachi and I. Matsuda},
journal= {arXiv preprint arXiv:2604.25450},
year = {2026}
}