Relativistic effects in the electronic structure of Cu{001}

Angle-resolved photoemission from Cu{001} with pure s-polarized light gives evidence for direct electron transitions from the 2 band, which are forbidden by the nonrelativistic dipole selection rules. The effect is explained by the mixing of additional orbitals into the relativistic-band basis set. Critical points for relativistic bands are =-2.85 0.10 eV, =-3.40 0.10 eV, =-3.70 0.10 eV, and are in good agreement with the results of the self-consistent relativistic-band-structure calculations of Eckardt, Fritsche, and Noffke. These observations confirm earlier reports by other workers which indicated that relativistic effects can play an important role in the electronic structure of first-row transition elements.