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2016-06 Germanene: breakthrough on the way to a room temperature 2D topological insulator

Success in preparing a single layer of germanium on a semiconducting MoS2 substrate is reported by the PIN group of Prof. Harold Zandvliet (Structural and Electronic Properties of Germanene on MoS2, PRL 2016). According to scanning tunneling spectroscopy and density functional theory (DFT) calculations this is the sought after germanene analogue of graphene. In a simultaneously published theoretical paper 2 Invariance of Germanene on MoS2 from First Principles also in PRL, Taher Amlaki combined an effective Hamiltonian approach with DFT calculations to study the topological nature of this system. The orientation of the germanene on MoS2 is predicted to play a crucial role in determining the topological character.

Crystalline carbon appears in two forms, diamond and graphite. Though both are thermodynamically stable, graphite has a slightly lower energy. For the other group IV elements silicon, germanium, tin and lead, it is the diamond structure that has the lower energy. Attempts to synthesize these heavier elements in the layered honeycomb form of graphite in order to study the single layer analogues of graphene have had limited success. Of particular importance is the preparation of so-called silicene, germanene or stanene on nonmetallic substrates in order to study transport properties. Unlike the original topological insulator system graphene, germanene is predicted to have a large spin-orbit coupling induced gap of 26 meV that would make observations possible at room temperature.

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