Dependence of electron correlation strength in Fe_1+yTe_1-xSe_x on Se content

The iron chalcogenide Fe_1+yTe_1-xSe_x on the Te-rich side is known to exhibit the strongest electron correlations among the Fe-based superconductors and is nonsuperconducting for x < 0.1. In order to understand the origin of such behaviors, we have performed angle-resolved photoemission spectroscopy studies of Fe_1+yTe_1-xSe_x (x=0,0.1,0.2, and 0.4). The obtained mass renormalization factors for different energy bands are qualitatively consistent with density functional theory and dynamical mean-field theory calculations. Our results provide evidence for strong orbital dependence of mass renormalization and systematic data which help us to resolve inconsistencies with other experimental data. The unusually strong orbital dependence of mass renormalization in Te-rich Fe_1+yTe_1-xSe_x arises from the dominant contribution to the Fermi surface of the dxy band, which is the most strongly correlated and may contribute to the suppression of superconductivity.