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Topological insulators: computational exploration of emerging electronic materials

Final Report Summary - TOPOMAT (Topological insulators: computational exploration of emerging electronic materials)

A number of realizations of novel topological electronic phases in materials have been discovered during the past decade. For instance, the so-called topological insulators are materials that have a bulk electronic band gap, but also exhibit conducting surface states as a result of non-trivial band structure topology induced by strong spin-orbit interactions. These peculiar surface states are characterized by a number of novel properties such as the linear band dispersion and helical spin textures with no spin degeneracy, which makes them immune to backscattering. Besides topological insulators, other topological phases such as Dirac and Weyl semimetals have been drawing continuous attention very recently. It is clear that topological materials are establishing themselves as novel, diverse major class of materials. Due to their extraordinary properties, topological materials are expected to find numerous technological applications, in particular in electronics and its prospective extensions – spintronics and quantum information processing.

The project explored these novel materials by performing computer simulations at various levels of complexity, ranging from model Hamiltonians to density functional theory and many-body perturbation theory techniques. The global objective is to provide theoretical support required to build a link between the fundamental properties of topological materials and their prospective technological application by investigating physics, chemistry, materials science, and device-related aspects of these materials. This objective was attacked in two different ways – by discovering novel topological materials and by investigating their novel properties and phenomena related to the topological nature.

The most important achievements are the following. First, we developed a methodology that realizes a systematic search of topological materials among known materials. This resulted in the prediction of a large number of candidate compounds, and the most appealing predictions were confirmed experimentally. The prominent examples are the quasi-one-dimensional topological insulator beta-Bi4I4, that is starting an entirely new class of bismuth halide topological materials, and robust Weyl semimetals MoP2 and WP2 that showed an extraordinary combination of physical properties. The discovered material have strong potential towards technological applications. Second, we investigated structure-property relations and the role of disorder in topological insulators. The gained understanding allows to fine-tune the properties of topological materials by changing chemical composition, introducing strain or various defect structures. Importantly, the project has enabled establishing joint activities with experimental research groups worldwide that was crucial for confirming our predictions.