FWF - Oberflächen - Exotic Surfaces

The present application seeks to understand the properties of novel and unusual surfaces, for which few dynamical measurements exist. The applicant plans to spend a research period of 24 months at the University of Cambridge in the Surface Physics Group under the supervision of Dr. William Allison. The research group of Dr. William Allison is the world's only group that operates a helium-3 spin-echo spectrometer which can resolve energy changes as small as 20 neV. Spin-echo measurements on the semimetal Bi(111) and the topological insulator PbBi2Te4(111) will provide new benchmark data that will assist in the development of theoretical approaches to understand the fundamental atom-surface interaction on semimetal and topological insulator surfaces. In particular the spin-echo technique is the only method that can provide data with sufficient experimental resolution for direct measurements of the mode-selected electron-phonon interaction. Furthermore, the possible investigation of acoustic surface plasmons in a spectral region inaccessible to any other technique, is an extremely attractive aspect not yet explored. Based on the analysis of the spin-echo measurements a theoretical concept for the He-Bi(111) interaction will be developed which may also be adapted for other semimetals. In an additional return phase of 12 months at the Institute of Experimental Physics (Graz University of Technology) the knowledge obtained in the group in Cambridge and the first application of this concept for the He-Bi(111) system will be further developed. This includes the interpretation of the He-PbBi2Te4(111) data measured in Cambridge. The data will be used to find an appropriate atom-surface interaction model for topological insulator surfaces. Finally the influence of adsorbed atomic hydrogen onto the Bi(111) surface with the heading phrase "the lightest on the heaviest" will be investigated experimentally. While an understanding of the model semimetal bismuth is of great interest for topological insulators and spintronics, topological insulators themselves are promising candidates for potential applications ranging from spintronics to quantum computation. Despite their great importance, especially in the case of topological insulators, semimetals have never been approached with helium atom scattering due to their intrinsic complexity of being surface conductors (even superconductors) and strongly corrugated at the same time. The applicant's expertise in helium scattering on these surface systems combined with the world-leading experimental facilities available in Cambridge will generate new understanding at a fundamental level to these promising materials. Ongoing cooperation with the University of Cambridge will provide continuous exchange of knowledge and the realization of joint experiments.