Relativistic effects on the surface electronic structure of Cu(001): Observation of a spin-orbit-gap surface state

A second Cu(001) M{} surface state located near the d-band maximum has been characterized using angle-resolved photoemission. High energy resolution, provided by a new dispersive spectrometer, was necessary to identify and characterize the surface state. At M{} the state, which has odd parity with respect to the (100) mirror plane, lies 65 meV below the d-band maximum, at 2.113 eV binding energy. Comparison with the surface projection of a recently calculated relativistic bulk band structure, indicates that this state lies in an absolute spin-orbit gap. The gap extends along one third of {Σ}{} in the surface Brillouin zone.