March 4, 2009 (HP17).  The Institute of Physics (IOP) and the German Physical Society (Deutsche Physikalische Gesellschaft, DPG) jointly launched in 1998 an open-access online journal for physics under the title “New Journal of Physics” (NJP), seehttp://www.iop.org/EJ/njp.  This peer-reviewed publication is supported by publication fees, but freely accessible to all readers.  In July 2006, Essential Science Indicators named NJP a Rising Star in the field of Physics—that is, the journal had the highest percent increase in total citations in this field. The journal’s current record includes over 800 papers cited a total of over 3,000 times.  Its present impact factor is 3.485.

The NJP publishes also “Focus Issues”, which concentrate on one especially timely topical area and are edited by invited guest editors.  Such paper collections might be updated by papers appearing in subsequent issues; the current status of a collection can be most conveniently retrieved.  In February 2009 appeared the issue “Focus on Iron-Based Superconductors”, edited and prefaced by Hideo Hosono and Zhi-An Ren (NJP, vol. 11).  We cite from their preface:

“In 2006 a new superconductor based on iron, LaFeOP, was discovered by a group at Tokyo Institute of Technology, Japan. Iron, as a ferromagnet, was believed to be the last element for the realization of superconductivity because of the way ferromagnetism competes against Cooper pair formation. Unexpectedly, however, the critical temperature remained at 4–6 K irrespective of hole/electron-doping. A large increase in theT_c to 26 K was then found in LaFe[O_1–xF_x]As by the same group (and was published on 23 February 2008, in the Journal of the American Chemical Society). TheT_c of this material was further raised to 43 K under a pressure of 2 GPa and scientists in China then achieved aT_c of 56 K at ambient pressure by replacing La with other rare earth ions with smaller radius—a critical temperature that is second only to the high T_c cuprates.
This fast progress has revitalized research within superconductivity and in 2008 there were more than seven international symposia specifically on Fe(Ni)-based superconductors. Through the rapid pace of research within the last year, iron-based superconductors have revealed several unique properties such as a high upper critical field and robustness to impurities. Participation of five 3d-orbitals in the Fermi levels also means that the electronic structure is complex compared with the cuprates.
As an aside, the first special issue on this subject was published in November 2008 in the Journal of the Physical Society of Japan (vol 77, supplement c) as the proceedings of the International Symposium on Iron-Pnictide Superconductors held in Tokyo on 29–30 June 2008. We would like to encourage the community to read both issues.”

The focused collection now contains 20 papers on various aspects of the subject, such as the crystal and electronic structure, pairing mechanisms, optical, electrical and magnetic properties, effects of dopants, etc., etc.   This issue represents a useful paper collection for those, who wish to become an up-to-date snapshot overview of this nascent area.  One can expect more papers to be added to the present collection.