$d$-wave superconducting gap observed in protect-annealed electron-doped cuprate superconductors Pr${}_{1.3-x}$La${}_{0.7}$Ce${}_x$CuO${}_4$

Abstract

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.