Engineering of Topological Spin States in Epitaxial Alpha-Tin Layers

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This project is addressing a new type of topological insulator (TI) which has thus far only been proposed theoretically. It is formed by strained alpha-Sn grown epitaxially on a semi-conducting InSb substrate. The principal feasibility of this TI has recently been demonstrated by our group. The epitaxial approach opens various pathways to study the properties of the Dirac surface state, including different surface orientations of the TI crystal. Particular interest rests on the evolution of the nature of the Dirac bands as a function of layer thickness. The in situ preparation also allows to decorate the surface with an additional coating layer, specifically with heavy or magnetic atoms, which will alter the spin-orbit interaction at the TI interface and affect the properties of the Dirac state.The experimental approach to unveil the electronic properties is based on high-resolution angle-resolved photoemission (ARPES). This permits to track changes in the band dispersion with thickness, ranging from gapped Rashba-type states to the fully topological regime with a Dirac crossing. The Fermi level of the TI can be controlled precisely by doping, which allows to monitor the band situation and the Fermi surface even significantly above the Dirac point. The spin-topology will be addressed by using spin-resolved ARPES, where the evolution with thickness and under the influence of a surface coating can be unveiled. The studies are furthermore backed by collaboration partners in the field of density functional and many-body theory.