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

Abstract

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, spinorbit 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 spinpolarized Rashba-split states spin can be effectively suppressed, so that only the ''classical'' magnetoconductance effect remains, as observed in this system.

Magnetoresistance Measurements of a Superconducting Surface State of In-Induced and Pb-Induced Structures on Si(111)

“…Using state-of-the-art techniques, it has now become possible to study the electronic transport phenomena in the surface states by conductivity measurements in ultrahigh vacuum [1][2][3][4][5][6] and describe the results from the band structures measured by angle-resolved photoemission spectroscopy [7]. Ultrathin metallic films grown on semiconductor substrates, especially superconducting ones, are also targets of active research of transport properties in relation to their structure and morphology [8][9][10][11][12][13][14][15][16]. However, there are no works that have performed magnetotransport measurements at subkelvin temperatures, which is likely needed to unravel the superconducting properties of surface superstructures.…”

Charge and spin transport on surfaces and atomic layers measured by multi-probe techniques

“…Furthermore, it has been now possible in the last decade to carry out the in situ transport measurements in UHV at very low temperatures (less than 1 K) under strong magnetic field (up to around 10 T) [18,19]. These UHV machines are based on low-temperature STM techniques under magnetic field.…”