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TT: Fachverband Tiefe Temperaturen

TT 40: Superconductivity: Ferropnictides 1

TT 40.14: Vortrag

Donnerstag, 26. März 2009, 17:45–18:00, HSZ 03

Interplay between crystal structure and magnetism in the superconducting AFe₂As₂ ( A = Ca, Sr, Ba and Eu) Systems: A First-principles Study — •Alim Ormeci, Deepa Kasinathan, Katrin Koch, Miriam Schmitt, and Helge Rosner — MPI CPfS, Dresden

Although the recently discovered FeAs-based superconducting compounds crystallize in different structures, they have the same Fe-As substructure and display very similar electronic properties including similar patterns of structural and magnetic transitions. However, experimentally important differences are also found between the REOFeAs (RE = rare-earth) and the AFe₂As₂ families. Because sample composition and quality are easier to control in the latter family, we focus on the AFe₂As₂ systems. Using all-electron full-potential calculations, we study the relation between the onset of spin-density wave (SDW) and the tetragonal-to-orthorhombic transition. We find that the SDW pattern is necessary for the structural transition to take place. We also explore how electronic structure and magnetic behavior change when all free structural parameters, As-z, c/a and a/b, are optimized at different unit cell volumes (pressures). All four systems are compared with each other based on the calculation results. Most calculated properties agree well with the measured properties, but several of them are rather sensitive to the As z position. For a microscopic understanding of the electronic structure of this new family of superconductors this structural feature is crucial, but its correct ab initio treatment still remains an open question.