Differentiation of electron doping and oxygen reduction in electron-doped cuprates

TL;DR

This study distinguishes the effects of electron doping and oxygen reduction in electron-doped cuprates using alkali-metal dosing and ARPES, revealing impurity oxygen's role in pseudogap formation.

Contribution

It demonstrates a method to separate electron doping effects from oxygen non-stoichiometry in cuprates, clarifying their individual impacts on electronic structure.

Findings

Alkali-metal deposition suppresses Fermi surface reconstruction due to antiferromagnetic order.

Pseudogap persists despite additional electrons from alkali-metal dosing.

Impurity oxygen atoms significantly contribute to pseudogap formation.

Abstract

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.