Orbital Dependent Band Renormalization in Fe$_{1+y}$Te$_{1-x}$Se$_{x}$

One of the important factors in understanding the Fe-based superconductor is their multi-orbital nature. In this study we present ARPES results on the iron chalcogenide Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ (known as the 11 system), the structurally simplest member in Fe-based superconductors. Our result shows that as Te substitutes Se, the Fe dxy orbital has seen a significant increase in the band renormalization while the other orbitals stay unchanged. Our discovery indicates that different orbitals in Fe-based superconductors have different correlation levels, evolve distinctively with crystal parameters and may play different roles in the emergence of superconductivity.