We have investigated the electronic structures of recently discovered superconductor FeSe by soft-x-ray and hard-x-ray photoemission spectroscopy with high bulk sensitivity. The large Fe 3d spectral weight is located in the vicinity of the Fermi level (EF), which is demonstrated to be a coherent quasi-particle peak. Compared with the results of the band structure calculation with local-density approximation, Fe 3d band narrowing and the energy shift of the band toward EF are found, suggesting an importance of the electron correlation effect in FeSe. The self energy correction provides the larger mass enhancement value (Z^-1=3.6) than in Fe-As superconductors and enables us to separate a incoherent part from the spectrum. These features are quite consistent with the results of recent dynamical mean-field calculations, in which the incoherent part is attributed to the lower Hubbard band.
@article{arxiv.1009.5496,
title = {Electron correlation in FeSe superconductor studied by bulk-sensitive photoemission spectroscopy},
author = {A. Yamasaki and Y. Matsui and S. Imada and K. Takase and H. Azuma and T. Muro and Y. Kato and A. Higashiya and A. Sekiyama and S. Suga and M. Yabashi and K. Tamasaku and T. Ishikawa and K. Terashima and H. Kobori and A. Sugimura and N. Umeyama and H. Sato and Y. Hara and N. Miyakawa and S. I. Ikeda},
journal= {arXiv preprint arXiv:1009.5496},
year = {2015}
}