Seminarium "Teoria i Modelowanie Nanostruktur"

During the last decade research on topological effects in condensed matter physics became one of the hottest areas of study. However, even though the experimental observation of the quantum spin Hall effect (QSHE) was reported for 2D non-magnetic topological insulators, the accuracy of conductance quantization is rather unsatisfactory and thus their applicability is limited. Therefore, it is important to look for new materials, whose properties would match the theoretical predictions. Recently, QSHE was proposed for 2D transition metal dichalcogenides in 1T’ structure[1]. The most stable compound of this class, tungsten ditelluride, is studied using numerical quantum transport simulations. Without strain, it is a semimetal with 0.1 eV band overlap, but if small strain is applied, the overlap can be removed. Atight-binding model is prepared in order to reproduce low-energy band structure obtained from first principles calculations. It is then used to study properties of the edge states, which reveals features such as a short decay length (about 5 nm). The simulations are performed for both unstrained and strained material and the topological protection of the edge states from disorder is shown. It results in quantized conductance for a broad range of disorder magnitudes, which confirms the viability of this material for device application.Reference:[1] X. Qian, J. Liu, L. Fu, and J. Li, Science 346, 1344 (2014)