Cu doping effects on the electronic structure of Fe1-xCuxSe

Using angle-resolved photoemission spectroscopy, we investigated the evolution of the electronic structure of Fe1-xCuxSe from x = 0 to 0.10. We found that the substitution of Fe by Cu introduces extra electron carriers. The hole bands near the Gamma point were observed to shift downward with increasing doping x and completely sank down below the Fermi level (E-F) for x >= 0.05. Meanwhile, the electron pockets near the M point became larger but lost the spectral weight near E-F. Concomitantly, the effective mass of the electron bands increased with doping. Our results show how a metal-insulator transition behavior occurs upon Cu doping in view of the electronic structure and provide a platform to further investigation on the origin of emergent magnetic fluctuation in Fe1-xCuxSe.