Recent discovery of iron-based high temperature superconductors has generated intense research activities in the fields of condensed matter physics, materials sciences and physical chemistry.  While only very limited solid understandings have been obtained and more puzzles are being unveiled, it has become clear that this new class of materials is a perfect host for the complex and rich condensed matter physics involving multiple physical effects with similar energy scales.
This talk will address the electronic and magnetic structure of the iron based superconductors, focusing on effects of the symmetries (and their violations) in the spin, charge, orbital and the translation degree of freedoms.  First, the magnetic structure will be discussed in connection with a hidden ferro-orbital order.  Second, the rich variety of magnetic orders found in the families of the parent compounds will be explained using a simple unified picture.  Third, the observed strong suppression of the ordered magnetic moment from the large local moment will be addressed, demonstrating the subtle roles of itinerant carriers.  Finally, novel physical effects of disorder will be discussed in a few case studies.
Referencees
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