Lay summary

Superconducting iron chalcogenides

For fifteen years after discovery of High Temperature Superconductivity by G. Bednorz and K.A. Müller, complex oxides of copper seemed to be the only group of materials showing this property. The situation changed in 2001 after the discovery of superconductivity in MgB2 and more recently (2008) in Fe-based compounds. As polarized iron spins were assumed to break the Cooper pairs accountable for superconductivity, this last discovery was absolutely unexpected. Among the iron-based superconductors iron chalcogenides e.g. FeSe have the simplest layered structure. The superconducting transition temperature (Tc) of the iron selenide FeSe is only 8K but increases to about 14K when doped with Te and to over 30K under pressure or intercalated by alkali metal.

The following tasks will be performed within the frame of the project:

      1.Synthesis of AFeSe single crystals with isovalent (Te, S) and non-isovalent (P, Sb) dopant on anion site (A = K, Rb, Cs).

      2.Investigations of alkali metal intercalated AFeSe with Se sites substituted by Te, S, P or Sb and Fe sites substituted with Mn and Sm (A = K, Rb, Cs).

      3.Studies of possible intercalations of FeSe with alkali earth cations.


The obtained samples will be investigated using different methods: magnetization, specific heat, Hall and Seebeck effects and muon-spin-rotation spectroscopy. Detailed structural studies will be carried out by means of X-ray powder, synchrotron X-ray single crystal and neutron diffraction techniques.

The purpose of the work will be a search for an optimum composition/stoichiometry in respect of the superconducting properties and to provide a contribution to the understanding of the superconducting state in this materials, especially coexistence of magnetism and superconductivity.