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Mads Hansen presents

 Search for- and study of new FeSi-superconductors

Friday, December 16th 2022 at 14:00

Room K223 – Building K – CNRS

Link visio : https://cnrs.zoom.us/j/97449389229?pwd=azRUOWlFZGNYMFE2Z0tTK25Qemk5Zz09

Meeting ID: 974 4938 9229 | Passcode: t05qWf

The defence will be in English.



In this thesis, the synthesis and characterization of FeSi-based superconductors is explored, more specifically the ZrCuSiAs type structures also known as 1111-type iron-based superconductors. The synthesis of LaFeSiH is investigated, using both a solid-gas reaction approach and high pressure synthesis methods, using thermal decomposition of high hydrogen density materials as a source of hydrogen, in a high volume press. Here, an orthorhombic distortion of the otherwise tetragonal LaFeSiH is reported with a chemical origin as the compound is proposed to have the chemical formula LaFeSiH1+x.
The structural and magnetic properties of LaFeSiH were also investigated using X-ray and neutron diffraction, showing the absence of a structural transition as well as a lack of long-range magnetic order within the sensitivity of the present experiments. Next, the discovery of the superconducting compound LaFeSiO is reported and a comprehensive study of the compound is presented, including neutron diffraction, magnetization, resistivity, nuclear magnetic resonance, and ab initio calculations. The distinct, hole-dominated Fermiology is discussed in the context of other iron-based superconductors such as isostructural arsendies.
A structural study of YFe2Si2 is then presented, exploring the structure at high pressure as well as at low temperature