Current issues of iron-based superconductors

There have been many issues which remain mysterious on the physics of high temperature superconductivity, magnetism and quantum criticality. The recent discovery of iron-based superconductors could enable physicists to break through the mystery of those issues. We review the recent works about the magnetic properties as well as the superconductivity. In addition, we investigate a new mechanism to understand the unconventional superconductivity and the quantum critical phenomena. A single universal model of strange metals coming from different theoretical approaches of quantum matter in the strongly interacting many-body systems is reviewed and applied to investigate the new discovered Fe-based superconductors and the AdS/CFT correspondence together with a gravity.