FWF - Chalcogenides - Transition Metal Chalcogenides under Extreme Pressures

The aim of this research project is to study the high-pressure phase diagram of transition metal chalcogenides (TMCs). We will search for new high-pressure structures, determine their superconducting properties, and investigate lattice instabilities. With respect to conventional superconductivity (SC), a highly topical class of compounds being intensely investigated at the moment are van der Waals (vdW) crystals, i.e., stacked materials whose sublayers are loosely held together by weak vdW forces. Prototypical examples for this class are the transition metal dichalcogenides (TMC2), and of particular interest with respect to SC are its metallic members, as the superconducting state coexists or appears in very close vicinity to a charge density wave (CDW) phase. (The electron density in a CDW forms a standing wave pattern and is accompanied by a periodic lattice distortion.) These two phases have originally be thought of as being mutually exclusive, since they both depend on the same interaction between electrons close to the Fermi energy and lattice vibrations. The coexistence of these two phases in TMC2 offers the exceptional opportunity to study the mutual influence of SC and CDW order. In the project we will employ evolutionary search methods to explore the high-pressure phase diagram of TMCs, with particular focus on identifying novel superconducting structures. We also envisage to use state-of-the-art methods to investigate the properties of the superconducting state within the CDW phase in several TMC2 completely from first-principles, and shed light on the effects of pressure on the electronic and vibrational structure, electron-phonon coupling, SC and charge-order. This project will contribute to obtain a more complete picture of the high-pressure phase diagram of TMC and similar materials, providing a solid foundation for future high-pressure research. The results of this project will also help to improve the understanding of the interactions between SC and charge order in TMC, and clarify the effects of high-pressure on atomic bonding, and the mechanisms behind SC and CDW order in these materials.