Oxygen-content-dependent electronic structures of electron-doped cuprates

We performed systematic angle-resolved photoemission studies on as-grown and oxygen-reduced electron-doped cuprates Pr${}_{0.85}$LaCe${}_{0.15}$CuO${}_{4}$, Nd${}_{1.85}$Ce${}_{0.15}$CuO${}_{4}$, and Sm${}_{1.85}$Ce${}_{0.15}$CuO${}_{4}$, in order to investigate the oxygen-reduction process. All of the as-grown systems we have studied show metallic edges in the antinodal region, while near ${E}_{F}$ nodal spectra are suppressed, resulting in partial gap opening. In addition, spectra from as-grown systems show weak and broad low-energy quasiparticle peaks (QPPs). Upon proper reduction, sharp QPPs emerge but they are strongly suppressed again in the over-reduced state. This QPP behavior deviates from the magnetism and doping-evolution origin of QPP suppression, and implies that scattering due to disorder and impurity is a more probable cause for the broken coherence of the quasiparticle state. Our results are also consistent with the recently proposed Cu-deficiency scenario.