Iron-based superconductors (IBSs) were discovered by H. Hosono’s group in early 2008 and received great attention in the superconductor community. The critical temperature (c) of IBSs increased to 55 K in SmFeAsO1-xFx. but the c has not increased anymore until now. The types of IBSs that have been investigated include a prototype series of five that show a common superconducting Fe-As (or Se) layer in the unit cell. The growth of IBS single crystals is a very important subject in research on superconductivity because the intrinsic properties of the materials without impurity must be known.
