Complex electronic structure of iron-based superconductors as a key to high temperature superconductivity

The iron based superconductors (FeSC) promise interesting physics and applications, and, while the interplay of superconductivity and magnetism, as well as their mechanisms remain the issues of active debates and studies, one thing in FeSC puzzle is clear, namely that it is the complex multi-band electronic structure of these compounds that determines their rich and puzzling properties [1, 2]. What is important and fascinating is that this complexity seems to play a positive role in the struggle for understanding the FeSC physics and also for search of the materials with higher Tc´s. This is because the multiple electronic bands and resulting complex Fermiology offer exceptionally rich playground for establishing useful empirical correlations. This is also because this electronic structure is well understood-the band structure calculations well reproduce its complexity: all the bands and their symmetry. The role of the experiment, in this case, is just to define the exact position and renormalization for each band. This piece of experimental knowledge, however, appears to be vitally important for understanding of the electronic properties of these new compounds.