The dominance of surfaces and interfaces: A view to magnetoconductance and structure in low-dimensional crystalline films



For ultra-thin films, electronic transport properties at surfaces and interfaces are dominated by electronic scattering at the interfaces. Therefore, as our example with Pb on Si(557) shows, d.c. transport is sensitive to confinement, to growth modes, and to (electronic) surface roughness. During the growth of Pb on Si(557) up to more than 10 monolayers, we found classical and quantum size effects, a pronounced conductance anisotropy and conductance oscillations directly related to the anisotropic layer-by-layer growth mode of the Pb film on this regularly stepped surface. In fact, it turned out that the interface anisotropy, which extends up to the seventh layer in conductance, is kept as a memory effect even for thick (isotropic) layers. By adding a magnetic field, details of the scattering mechanism at impurities and defects are revealed, since elastic, inelastic, spin–orbit scattering contributions can be separated.

Strong changes of scattering properties are evident when going from the multilayers to the monolayer, as demonstrated again for the system Pb on Si(557). Contrary to multilayers, spin–orbit scattering dominates for the monolayer, presumably due to the symmetry reduction at the surface and the appearance of spin-split bands split by the Rashba effect. Also the anomaly in spin–orbit scattering close to monolayer completion, coupled with quasi one-dimensional d.c. conductance, can be ascribed to the Rashba effect. The intriguing interplay between bulk and surface conductance with large Rashba split states at the surface is exemplified by a study of multilayer growth of Bi on Si(111). By magnetoconductance we were able to separate bulk from surface contributions. Scattering between strongly spin-polarized Rashba-split states spin can be effectively suppressed, so that only the “classical” magnetoconductance effect remains, as observed in this system.