Neutron scattering investigation of iron pnictides superconductors

• Applicant: Dr. Karel Prokes, since 5/2012
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2010 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 168598494

In the so-called exotic superconductors, formation of a superconducting condensate of cooper pairs is mediated by magnetic fluctuations. Two classes of materials with transition temperatures at opposite extremes are known. In the d−electron cuprate materials, superconductivity emerges from a charge doped antiferromagnetic insulator with Tc as high as 160 K. At the other end of the scale, in the f−electron superconductors, the groundstate is easily tuned between itinerant spin density wave (SDW) magnetic order and superconductivity with Tc~1 K. The recently discovered FeAs superconductors bridge this gap with Tcs of up to 55 K and a parent phase which has unambigously been shown to be a SDW metal. Early investigation of the pnictides have identified the SDW instability in the parent compounds as a critical feature in understanding the behavior of these materials. This itinerant view has shed light into the coupled structure and magnetic transition of the parent compounds and provided a robust model for the symmetry of the superconducting order parameter. Despite these successes the role of strongly localized physics is evident in the such observations as the co-existance of magnetism and superconductivity or optical spectroscopy. One remarkable feature of the pnictides is that they can be tuned into the superconducting state using pressure, in sharp contrast to their cuprates counterparts. This behavior provides us with two tuning parameters to achieve superconductivity as well as a new means probe the underlying physics of these materials. We propose that considerable progress can be made in understanding the route to superconductivity in the iron pnictides by closely examining the development of magnetism as both a function of pressure and chemical doping. These two parameters that tune superconductivity have the possibility of accessing decisively different physics. The onset of superconductivity or its enormous enhancement under relative modest pressure provides a markedly different means in tuning the system to superconductivity in the absence of chemical disorder. We believe that the contrast between these two tuning parameters can shed light into this dichotomy between the relevance of itinerant and strongly correlated physics. We shall focus our investigation to the simplest of the iron pnictide superconductors, the FeTe1−x Sex system as they are chemically simple, superconducting Tc’s are relatively high and relatively large high quality single crystals are available.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1458: High Temperature Superconductivity in Iron Pnictides
• Ehemaliger Antragsteller: Dr. Dimitri Argyriou, until 5/2012