Transport measurements, structure and Mössbauer investigations of FeSe-related novel superconductors under high pressure up to 100GPa

• Applicants: Dr. Vadim Ksenofontov; Dr. Sergiy Medvediev
• Subject Area: Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: from 2010 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 167738825

This project focuses on the investigation of the transport properties of FeSe and related compoundsunder high pressure. FeSe is the simplest of the recently discovered superconductors andcan serve therefore as a model system to gain insight into the mechanism of superconductivityand the structure to property relation of the iron pnictides, iron chalcogenides and related compounds.FeSe is superconducting in the parent phase, no doping is necessary; even more the superconductivity depends strongly on the exact stoichiometry. Different from the arsenides, atetragonal to orthorhombic transition is connected with the superconducting phase. Superconductivitydisappears under pressure, when FeSe transforms reversible into a NiAs-type structure. Nostatic magnetism is observed over the whole pressure vs. temperature phase diagram, measuredby 57Fe-Mössbauer spectroscopy. However, 77Se-NMR spectroscopy gives evidence for shortrange magnetic fluctuations. To solve the question whether magnetism, spin fluctuations, quantumcriticality and/or phonons are important in FeSe we want to investigate structure, magnetism,density of phonon states and resistivity as a function of pressure, magnetic field and temperature.The systems under investigation will be simple model systems such as FeSe, FeSe1-xTex, FeSe1-xSx, CuxFe1-x Se, RuxFe 1-x Se, FeSe–CoAs, TlFe2Se 2-x Asx. The goal is to complete thephase diagram of FeSe and to solve the above addressed questions.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1458: High Temperature Superconductivity in Iron Pnictides
• Participating Person: Professorin Dr. Claudia Felser