Films of iron chalcogenide superconductors

Iron chalcogenides are of great interest for both basic physics and high-field applications. Although their superconducting transition temperatures are typically lower than those of iron pnictides, iron chalcogenides exhibit lower anisotropies with very high upper critical field slopes near the superconducting transition temperatures. They also have the simplest structures among the iron-based superconductors. This review covers recent progress in the field of superconducting thin films of iron chalcogenides, with primary focus on FeSe_1-xTe_x (0 ≤ x ≤ 1). High quality superconducting thin films with x = 0 and 0.5 have been fabricated by several groups. Of particular interest is that some of them exhibit significantly higher superconducting transition temperatures than those of bulk polycrystalline samples and single crystals over the entire doping regime. Upon the incorporation of small amounts of oxygen, superconductivity is seen to emerge in a thin film of FeTe (parent compound of the iron chalcogenides), but not in the bulk. Advances in superconducting-tape fabrication of iron chalcogenides are also described since the very high upper critical fields and critical current densities of these films suggest that they are prospective candidates for high-field applications. In addition, we present a brief comparison between iron chalcogenide films and iron pnictide films.