2017 Volume 52 Issue 6 Pages 422-432
This article reviews the developments over the past 10 years in the thin film growth of Fe-based superconductors, including recent topics of interest in this field. At the beginning of the research, there was pessimism that thin films of the highest-Tc compound, LnFeAs(O,F), would not be easy to grow since it is composed of five elements, namely two cations and three anions. The situation is different from cuprates such as Bi2Sr2CaCuO8, which also consists of five elements, but four cations and one anion. Indeed, there were enormous struggles in the initial attempts to grow LnFeAs(O,F) using pulsed laser deposition. But a major breakthrough was achieved using molecular beam epitaxy, and now LnFeAs(O,F) films with Tcend over 55 K are routinely grown, at least in Japan. The current best films of many of Fe-based superconductors show superconducting properties substantially superior to those of bulk single crystals. Furthermore the simplest material among Fe-based superconductors, FeSe, whose bulk Tc is as low as 8 K, is opening up a new frontier. The Tc of ultra-thin FeSe films are as high as 40 K or possibly it may even reach >100 K in the form of single atomic-layer films.
