Observation of ad-like Surface-State Band on Cu(100) using Resolved Photoemission

A narrow peak (full width at half maximum about 60 meV) just above the top of the bulk $d$ bands has been observed in angle-resolved energy distribution curves of Cu(100). The peak is attributed to a $d$-like surface state in an energy gap of the projected bulk band structure near the symmetry point $\overline{M}$ of the two-dimensional Brillouin zone. A surface state near $\overline{M}$ was predicted in recent self-consistent calculations.