Magneto-elastic couplings and superconductivity in 11-type chalcogenides: Thermal and quantum fluctuations

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The parent Fe1+yTe compound of the 11-type chalcogenide superconductors has a rieh phase diagram with temperature-induced structural and magnetic phase transitions in dependence of tuning parameters such äs amount of excess Fe or hydrostatic pressure. We would like to investigate the nature of different symmetry breaking phase transitions and unusual couplings between magnetic and structural order parameters in this System. Various tuning parameters, such äs, temperature, pressure, magnetic field, and chemical composition, will be used to explore the phase diagrams and locate possible quantum phase transitions. Forthis purpose, high purity single crystals of both superconducting and non-superconducting 11- chalcogenides will be synthesized with a precise control over the composition. High-pressure Synchrotron x-ray diffraction will be used to determine the lattice instabilities. Scanning tunneling microscopy (STM) and spectroscopy (STS), neutron scattering and x-ray absorption spectroscopy will be used to investigate the unusual interplay of local and itinerant magnetism. Since STM is sensitive to the Charge, any spin-orbit coupling or orbital ordering can be directly observed in the form of a modulated Charge density in an STM Image. The influence of magneto-elastic couplings on temperature or pressure-induced successive magnetic and structural phase transitions in the vicinity of superconductivity will be investigated using a combination of local as well as bulk experimental probes with collaborations within this priority program. This investigation is expected to differentiate roles played by lattice instabilities and spin fluctuatiops and shed light onto the pairing mechanisms for superconductivity in this System.