Topological Insulators: A study of bulk crystalline and Nanomaterials

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Topological Insulators (TIs) are a class of quantum materials that exhibit topological surface states. These materials are usually small band gap semiconductors where the bulk of the material is insulating, but they exhibit special surface states that are conducting and topologically protected. The materials are usually made of heavy atoms that give rise to strong spin-orbit coupling and this leads to the formation of surface states that are not destroyed by scattering or impurities. TIs are proving to be ideal materials for study in condensed matter physics, as the physics of these materials is novel and they offer huge scope for developing new theories and for the discovery of new materials. Although the TIs have gapless edge or surface states that are protected and are in theory supposed to have an insulating gap in the bulk, most of the 3D TIs discovered to date are still fairly conducting in the bulk. Materials design and processing have emerged as being key to the investigation and the discovery of new TIs. The challenge for materials physicists is to create TI materials that are true insulators in the bulk, in order to facilitate the study of their exotic surface states.In this proposal, we describe the methodology to be adopted to obtain high quality materials, for the different experiments proposed. We propose to synthesize a range of materials, some of which are already known to be Topological Insulators and other new materials such as the Topological Crystalline Insulators (TCIs) and those with emerging topological behaviour. The project will investigate both bulk crystalline materials and nanomaterials (in the form of nanoplatelets and nanorods). The study of the emergence of superconductivity in the 3D TIs and TCIs will be undertaken. The existence of a full pairing gap in the bulk in the superconducting Topological Insulators, together with the gapless surface states in these materials, makes them extremely interesting.The physics of these materials will be investigated through detailed studies of the bulk properties of the crystals (including resistivity and Hall effect, magnetisation, heat capacity) in particular, to understand the influence that the bulk electronic and magnetic properties have on their topological behaviour. X-ray/electron diffraction and electron microscopy techniques will be used for the investigation of the structural properties of both the crystals and nanomaterials. Investigations of the surfaces of the crystalline and nanomaterials by XPS and ARPES will be carried out with our collaborators. Neutron scattering and muon spectroscopy techniques will also be employed. Valuable theoretical input from the Project Partner will be used in conjunction with the results from the experimental investigations, to inform the decisions for the design and fabrication of new materials exhibiting TI behaviour.A wide network of experts, including both therorists and experimentalists, as collaborators will contribute to successfully deliver the work described this project.