  For electron-doped cuprates, the strong suppression of antiferromagnetic spin
correlation by efficient reduction annealing by the "protect-annealing" method
leads to superconductivity not only with lower Ce concentrations but also with
higher transition temperatures. To reveal the nature of this superconducting
state, we have performed angle-resolved photoemission spectroscopy measurements
of protect-annealed electron-doped superconductors
Pr$_{1.3-x}$La$_{0.7}$Ce$_{x}$CuO$_{4}$ and directly investigated the
superconducting gap. The gap was found to be consistent with $d$-wave symmetry,
suggesting that strong electron correlation persists and hence
antiferromagnetic spin fluctuations remain a candidate that mediates Copper
pairing in the protect-annealed electron-doped cuprates.
