Superconducting properties of iron chalcogenide thin films

Iron chalcogenides, binary FeSe, FeTe and ternary FeTexSe1-x, FeTexS1-x and FeTe:O-x, are the simplest compounds amongst the recently discovered iron-based superconductors. Thin films of iron chalcogenides present many attractive features that are covered in this review, such as: (i) easy fabrication and epitaxial growth on common single-crystal substrates; (ii) strong enhancement of superconducting transition temperature with respect to the bulk parent compounds (in FeTe0.5Se0.5, zero-resistance transition temperature T-c0(bulk) = 13.5 K, but T-c0(film) = 19 K on LaAlO3 substrate); (iii) high critical current density (J(c) similar to 0.5 x 10(6) A cm(2) at 4.2 K and 0 T for FeTe0.5Se0.5 film deposited on CaF2, and similar values on flexible metallic substrates (Hastelloy tapes buffered by ion-beam assisted deposition) with a weak dependence on magnetic field; (iv) high upper critical field (similar to 50 T for FeTe0.5Se0.5, B-c2(0), with a low anisotropy, gamma similar to 2). These highlights explain why thin films of iron chalcogenides have been widely studied in recent years and are considered as promising materials for applications requiring high magnetic fields (20-50 T) and low temperatures (2-10 K).