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Influence of the spin-orbit coupling of the BiAg2 surface alloy on electron scattering

AutorLobo-Checa, Jorge ; Schiller, Frederik ; Gambardella, Pietro; Ortega, J. Enrique ; Mugarza, Aitor
Fecha de publicación2013
CitaciónIVC-19/ICN+T (2013)
ResumenTransport properties of the solid are interweaved to its electronic wavefunctions. Further inside into them can be achieved through the study of scattering processes at defects, such as adsorbates or steps. The inelastic lifetime and quantum coherence are dependent upon the nature of the system, i.e, the type of defect, the chemistry, and the morphology of the Brillouin zones. Unraveling the fundamental scattering aspects of electronic states which exhibit no spin degeneracy is nowadays a key goal in the Solid State scientific community. An observation that has fostered this research activity is the lack of back-reflected waves near steps at the surface of topological insulators. The reduction of scattering has been attributed to the topological protection of surface states in the material, which is directly related to the strong spin-orbit interaction. In order to further understand the effect of spin-orbit coupling on the scattering phenomena, we have investigated by angle resolved photoemission (ARPES) the surface alloy of BiAg2. This system exhibits a giant spin-orbit splitting, that is orders of magnitude larger than, e.g., in semiconductor heterostructures. The spin-splitting is originated from the Rashba-Bychkov effect at the surface-vacuum interface and, in contrast to the topological insulators, the spin-orbit coupling strength can be tuned by alloying. We investigate the BiAg2 surface alloy within the scattering analysis framework previously performed on a Ag(111) curved crystal. The beauty of this substrate is that the density of steps changes progressively as we move along the curvature of the crystal so that the terrace size is continuously tuned from 400 nm to just 10 nm. Our results show unambiguously that the scattering of the surface electron wavefunctions by the steps is rather weak, much smaller than the underlying substrate of Ag with values of transmission close to the topological insulators. Furtherm ore, three different type of molecules deposited onto this surface alloy are not observed to interact with the spin-split BiAg2 states. We assign this unexpected behavior to the large spin-orbit coupling that protects these electronic states from impurities, in a similar fashion to the topologically protected surface states in topological insulators.
DescripciónTrabajo presentado a la "19th International Vacuum Congress" y a la "International Conference on Nanoscience and Technology", celebradas en Paris (Francia) del 9 al 13 de Septiembre de 2013.
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