![]() ![]() Moreover, we show that the robust, topological edge states disappear for a sufficiently high electric field.Īll together, we have found no indications for the QSH effect in thin film BST. With scanning tunneling spectroscopy experiments we show that the size of the gap depends linearly on the application of a perpendicular electric field and that this results in a topological phase transition. Due to the buckled honeycomb structure of germanene, this leads to broken inversion symmetry and charge will shift from one sublattice to the other. This is much lower that the workfunction of a regular scanning tunneling microscopy tip, and therefore results in a substantial electric field in the tunnel barrier. Furthermore, scanning tunneling spectroscopy experiments confirm that the Dirac point is located in close proximity to the bulk valence band, making it difficult to observe signatures of the QSH state.įor germanene, we determine a workfunction of 3.8 eV by measuring the image potential states. All together, the states give rise to prominent oscillations in the local density of states. We show that thin film BST displays well-defined topological surface states, surface states caused by the outermost Te atomic layer and quantized bulk energy levels. The electronic structure of both materials is thoroughly investigated using scanning tunneling spectroscopy. This research focuses on two theoretically predicted quantum spin Hall insulators, namely, germanene and thin film (Bi 0.4Sb 0.6) 2Te 3 (BST). ![]() This is a quantum state of matter characterized by two topologically protected, spin-polarized metallic states at the edges of a two-dimensional topological insulator. Particularly the quantum spin Hall (QSH) effect has been in the spotlights. As a result, researchers have shown an increased interest in topological insulators, because of their potential use in dissipationless electronics. The need to reduce energy consumption is now recognized worldwide. Bampoulis from the faculty of Science & Technology. Carolien Castenmiller is a PhD student in the department Physics of Interfaces and Nanomaterials.
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