High-resolution photoemission study of FeSr2YCu2O7+δ Original Research Article

We have performed high-resolution photoemission spectroscopy (PES) on FeSr2YCu2O7+δ, of which superconductivity of Tc=49 K was recently reported. We clearly observed opening of a d-wave-like superconducting gap and estimated the maximum gap value (Δmax) to be 10 meV at 15 K. This gap value gives 2Δmax/kBTc∼5, suggesting a strong-coupling nature of superconductivity in FeSr2YCu2O7+δ. Comparative PES study with superconducting and insulating samples shows that the valence band is rigidly shifted as a function of doping without evolution of additional states within the insulating gap.