Preface to the special issue ‘Focus on 10 Years of Iron-Based Superconductors’

In historical/archaeological terms, the iron age began around the 12th century BC and lasted over a millennium, up to the onset of historiographical records. The key role of iron in improving the life of human beings was established with the production of tools and weaponry by ferrous metallurgy. According to Greek mythology, among the five Ages of Man representing the stages of human existence on the Earth, the last one is the mythological iron age, where moral values and well-being eventually decline. Moving away from such awesome themes and blurred chronology, we focus on the well-defined era of iron superconductivity: it started in the early 2008, with the discovery of a superconducting transition at 26K in the LaO1-xFxFeAs compound by the Hideo Hosono group and it has now come to its tenth anniversary, with no sign of fading vitality. Also in this context, it was clear since the very beginning that iron was bound to play a primary role: on one hand it defied the shared belief about antagonistic relationship between magnetism and superconductivity and on the other hand it reignited new excitement about mechanisms and perspectives of unconventional superconductivity, over 30 years after the discovery of high-Tc in copper oxides Such ten year period may represent infancy form the commercial and technological application perspective, though early maturity from the scientific research point of view. Certainly it is a milestone which first of all deserves celebration, secondly calls for an assessment of the worldwide status of research on this topic, and finally allows a realistic, though still tentative, evaluation of the perspective potential in specific applications. This multifold aim is addressed by this focus issue, whose scope is collecting contributions from acknowledged researchers in the scientific community about the most relevant topics related to iron-based superconductors, state-of-the-art results and reviews, covering fundamental issues, applications, physical mechanisms, properties, compounds.