Valence-band splitting in Mg/W(110): Neither spin-orbit nor parity effect

Spin-orbit coupling, e.g., in the form of the Rashba effect, is of high interest due to its role in novel spintronic devices. In connection with the question whether spin-orbit splittings can be induced in a thin film by a buried interface, there is a current controversy as to the origin of measured energy splittings in Mg quantum-well films on W(110) [C. Koitzsch , Phys. Rev. Lett. 95, 126401 (2005); F. Schiller , ibid. 95, 126402 (2005)]. This problem is resolved by comparing Mg/W(110) with Mg/Mo(110) data. At variance with both previous reports, strong interaction of Mg states with surface states of the substrate is identified as the origin of the observations in question.