Large spin-orbit splitting of surface states in ultrathin Au (111) films

Spin-orbit (SO) splitting of surface states in ultrathin Au films was examined on the basis of density-functional theory. Due to the interaction between the top and the bottom Au layers, the SO splitting in the Au (111) films with few atomic layers is usually negligible. The splitting is, however, detectable if one surface of the film is terminated by adatoms, such as Al or H atoms. Similar effect can also be achieved if an external electric field is applied perpendicular to the surface. In addition, an interesting even-odd oscillating behavior in the SO splitting can be observed in a Au/Al interlaced structure. All these can be explained by the inversion-symmetry breaking. Our work provides a deep understanding of the SO effect in ultrathin heavy-metal films, which will be helpful in future all-electric spintronics.