Low-dimensional electronic magneto-transport in epitaxial ultra-thin Bi and Bi-Sb alloy films: impurities, structure, confinement and disorder.

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Our knowledge of electronic transport along spin-polarized states at surfaces and interfaces and its coupling with their structure and with defects on the atomic scale is still surprisingly incomplete. Therefore, the scattering properties of impurities with various magnetic moments in surface magneto-transport will be investigated in this project on ultrathin crystalline and epitaxially grown Bi-films, and on Bi-Sb alloys, which exhibit strong electron correlation with strong spin polarization due to the Rashba effect. Since Bi-Sb alloys switch in a certain range of concentrations into the regime of topological insulators, we will be able to compare surface conductance properties of trivial and topologically protected surfaces. Carrying out magneto-transport measurements in magnetic fields up to 4 T and in the temperature range between 5 and 300 K, coupled with Low Energy Electron Diffraction (LEED), we aim at the quantification of impurity-induced modifications of surface conductance. Thus we want to clarify the interdependence of, e.g., local magnetic moments of impurities, local symmetry of adsorption sites, charge transfer, and modifications of band structure, just to name a few relevant interconnections. We will extend the studies to test these concepts for topological insulator surfaces in BiSb alloys. In particular we will study robustness of surface state conductance. Finally we want to study the scattering properties of one-dimensional edge states by growth of stepped films with various surface orientations (Bi(111), (110) and (221)).