Introduction to the Special Issue—Selected Contributions to the 4th International Conference on Fundamental Problems of High Temperature Superconductivity (FPS’11)

Abstract

The problem of High Temperature Superconductivity remains highly topical: quite regularly novel HTS materials come on stage (copper oxide high-Tc superconductors in 1986, magnesium diboride in 2001, iron pnictide and iron chalcogenide compounds in 2008). Achieving progressively higher superconducting transition temperatures remains an encouraging motivation for researchers in the field. Up to now, Tc is the highest in copper-oxide perovskite materials with values higher than 150 K achieved in the 1980s and 1990s. Nevertheless, a commonly accepted approach to the problem of high temperature superconductivity is still missing. Discovery of superconductivity in iron pnictides with Tc’s up to 56 K introduced a new family of high-Tc superconductors. Their study and comparison with copper oxides provides an excellent chance to reveal the mechanism of high-Tc superconductivity in general, and in the two families, in particular. Cuprate superconductors are strongly correlated materials. The correlations lead to the anomalous properties of cuprates in the normal state and to the inapplicability of the Fermi-liquid model to their normal properties. In contrast, the iron-based pnictides in the superconducting state show signatures of weak rather than strong coupling. In the normal state, they seem to behave in accord with the Fermi liquid model. Contrary to cuprates, where an effective one-band electronic conduction model is sufficient to describe the low-energy electronic excitations, in the Fe-based compounds at least four bands contribute to superconduc-