PNICTIDES

The recent discovery of superconductivity (SC) in the iron pnictides (FePns) has generated great excitement in the scientific community since they appear as a new class of materials with high temperature superconductivity and present high potential for applications. Intensive research efforts are under way in the world to investigate the physical properties of these new exciting materials, which are interesting both in their own right and because they provide a new insight into other classes of superconductors. The iron pnictides share some similarities with the cuprates in that they are quasi two-dimensional and have antiferromagnetic parent compounds. Superconductivity in the iron pnictides can be induced from their antiferromagnetic parents by electron or hole doping via chemical substitution or by application of pressure. The proximity of superconductivity and antiferromagnetism suggests that the pairing mechanism in the doped FePns is related, as in cuprates, to the spin degrees of freedom. However despite the similarities of their phase diagrams, it is already well established that the underlying physics in these compounds is different. In contrast to the effective single-band character of the Cu 3dx2-y2 states in the cuprates, the multiband character of the Fe 3d bands brings some originality in the behavior of these materials. The purpose of this project is to understand the salient features of these compounds by preparing well characterized samples in the different families and using a series of complementary experimental tools in association with theoretical developments. The strong and original combination between material synthesis, macroscopic and local investigation techniques as well as theoretical calculations is quite unique and constitutes our strength in this highly competitive international field. This should in particular allow us to bring out interesting information on the electronic structure of these FePns through a combination of ARPES, transport measurements and band structure calculations, on the microscopic nature of the magnetic state through NMR and Mössbauer spectroscopy data, on the electronic scattering processes in the transport properties, and on the symmetry of the superconducting order parameter through combined ARPES and Raman scattering experiments. The different research teams involved in this project have acquired in the past an international recognition in the field of unconventional superconductivity and strongly correlated electron systems. We have been used to work in close collaboration since several years, which allowed us to start working in common very efficiently on these FEPns. The funding of this ANR project is essential to give us the opportunity to put some emphasis on this challenging topic, to establish a significant position of the French community in this highly competitive field, and give us a possibility to attract the best international scholars.