DFG-RSF: Impact of topology on electronic properties of ordered materials

• Applicant: Professor Dr. Jeroen van den Brink
• Subject Area: Theoretical Condensed Matter Physics ; Experimental Condensed Matter Physics
• Term: from 2016 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 310371528

The problem of novel material engineering is highly topical due to its potential impact on environment, natural resources saving, progress in telecommunications, and life quality, in total. In spite of almost 30 years history of cuprate HTS, the phase diagram and properties of the layered HTS materials are lacking of complete understanding, particularly in the vicinity of the quantum critical point. There are still debated the effects of the spin and orbital fluctuations, spin and charge ordering, many body effects (in the vicinity of the Lifshitz topological transition), and topology of the surface states (flat bands). Clearly, the role of potentially favorable factors for HTS must be clarified for the purposeful searching and engineering novel HTS materials. The current project aims at theoretical development and experimental implementation of the superconductors engineering based on layered materials (both pnictide, and dichalcogenide-based), studying their properties in the vicinity of QCP, clarifying the role of the interplay of magnetic ions ordering, charge ordering and SC pairing. The main idea of the project consists in studying and use of the flat band materials, both topologically trivial, and non-trivial. The former are to result in the enhanced contribution of the many-body condensation energy to the SC gap due to the proximity to the Lifshitz transition, the latter due to the non-trivial topology (Weyl semimetals). The flat band conditions in the topologically non-trivial materials is expected to be tuned using the band engineering methods (hydrostatic pressure, chemical and electric doping). The experimental and theoretical studies will be carried out in several related directions: (A) refining the theory and collecting new experimental data on the properties of Fe-HTS in the vicinity of the topological Lifshitz transition and in the vicinity of the anticipated QCP. (B) Studies of the new superconducting transition metal dichalcogenides, particularly, with topologically nontrivial spectrum. (C) Design, syntheses and studies of the true 3D topological insulator materials as a platform for studying and utilizing topologically protected surface states. The materials and structures will be synthesized by the solid state synthesis technique, growth from melt, by physical vapor transport, and also by the pulsed laser deposition techniques (PLD/MBE). The project includes development of the novel techniques for measurements and material diagnostics, complemental to the ordinary transport and optical methods. The research will be performed by the team consisting of experts in the complementary fields theoretical physics, and experimental chemistry and physicists.

• DFG Programme: Research Grants
• International Connection: Russia
• Partner Organisation: Russian Science Foundation
• Cooperation Partner: Professor Dr. Grigori Volovik
• Co-Investigator: Dr. Dmitri Efremov