Lanthanide substitution effects in electron-doped High-Tc superconductors studied by angle-resolved photoemission spectroscopy

We have performed an angle-resolved photoemission study of the electron-doped high-T (c) superconductors (HTSCs) Sm1.85Ce0.15CuO4 (SCCO) and Eu1.85Ce0.15CuO4 (ECCO). Around the nodal point (k) over right arrow similar to(pi/2,pi/2), we observed an energy gap at the Fermi level (E-F) for both samples, resulting from the strong effects of antiferromagnetism. The magnitude of this gap in ECCO is larger than that in SCCO, implying that the effects of antiferromagnetism in ECCO are stronger than that in SCCO. Also, we quantitatively confirmed the effects of antiferromagnetism by the band dispersions to tight-binding calculation.