Study of the new layered superconductors based on iron in tetrahedral coordination – TETRAFER

The recent discovery of superconductivity in layered compounds with iron in tetrahedral coordination has opened an extraordinary field of research. We have, on one side, the unusual encounter with superconductivity in materials prone to antiferromagnetic ground states, that suggests unconventional origins for the superconducting pairing. On the other, the variety of the possible compounds that may exhibited the similar conditions for both superconductivity and antiferromagnetism is large, the more so as compounds with Ni or Co replacing Fe can be placed in the same category. There seems to be work for several years in an atmosphere resembling that of cuprate research. The participants in this project have all an ample curriculum in the study of new superconducting materials. To cite only a few, the highest attained superconducting Tc, 166K in fluorinated Hg-1223 at 26GPa, the first evidence for two superconducting phases in UPt3, and one of the first confirmations for the existence of two gaps in MgB2. The magnitude of the challenge posed by tetrahedral iron superconductors has invited us to join together into a well-organized effort to ensure a lead in this central field. The demands of this project are proportional to the importance of the issues at stake, namely, theoretical understanding of superconductivity for high temperature superconductors and new technologically valuable materials. This has been long ago understood by competing japanese and chinese science administrators that have massively and recurrently invested in superconducting laboratories rendering most of our equipments practically obsolete in comparison. As an example of the unquestionable consequences, the last three important superconductors, MgB2, cobaltites and iron compounds have been discovered by japanese groups, while more than twenty years ago cuprates or organic superconductors were discovered in Europe. 1) We must ensure the development of the solid chemistry of iron superconductors, centring in the advantages of synthesis under high pressure, electrochemical intercalation, crystal growing and overall characterisation, all techniques where our laboratory excels. Its funding will allow a extensive research in the field. 2) The properties of materials are the consequence of the setting and the interactions of the atoms in the material. Together with chemical induced changes, pressure is the major parameter that allows the understanding of the relative importance of most factors controlling the material properties, as it changes both the distance between atoms and also the position of the atoms during phase transformations. A comprehensive view under pressure of physical properties such as electrical resistivity, magnetic susceptibility or specific heat combined with the evolution of the structure and lattice excitations such as phonons is a priceless tool in the search of new materials and in the understanding of mechanism responsible for the properties of the material. The project requests funding to upgrade existing equipment and develop new ones such as X-rays and Raman scattering measurements under pressure in order to form an unique in the world high pressure facility. 3) Once the new materials are optimized and state of the art samples have been synthesized, profound measurements of the superconducting fundamental properties will be performed in order to determine the gap symmetry, the number of possible gaps and in final resort the origin of the superconducting attraction, if these materials are not as elusive as cuprates. 4) A theory group with experience in magnetism, superconductivity and structural instabilities will on one hand, follow and interpret the obtained results and on the other develop new ideas that may contribute to the progress in material research.