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The role of electron correlation effects in the electronic structure of Ni-metal has been attracting interest for a long time. Here we present an extensive scanning tunneling microscopy and spectroscopy investigation on Ni(111) at low temperature which shows a parabolic surface state with a surprisingly low effective mass compared to the noble metals like Au, Ag and Cu and a d-surface resonance showing an electron-electron interaction signature which can be understood by a many-body calculation of the electronic structure (DMFT). For the first time, a small energy shift and a significant broadening of the electron state due to electron-electron correlation effects are obtained in a STM experiment. This opens the possibility to study electron many-body effects of surface states in detail with a very high energy resolution on a clean and defect free part of the surface. |