Surface state vs orbital Kondo resonance at Cr(001): Arguments for a surface state interpretation

We have performed a combined scanning tunneling spectroscopy, photoemission, and inverse photoemission study of the surface electronic structure of Cr(001). Our results show three surface-related features, one below, one above, and one right at the Fermi level E(F). While the surface-sensitive features below and above the Fermi level show characteristics of d(xz,yz) orbital symmetry, the feature right at E(F) exhibits predominantly d(z)(2)-like orbital symmetry. Upon exposure to oxygen, its spectral weight continuously shifts into the unoccupied electronic states. These results are in conflict with the interpretation of this peak as orbital Kondo resonance but point toward a Shockley-type surface state.