We report on fully epitaxial FeSe0.5Te0.5 (FST) thin films with high-quality grown on CaF2 (00l) substrate at a low temperature of 300°C by pulsed laser deposition. The transport Jc of thin films is up to 1.36 MA/cm 2 in self-field and 0.97 MA/cm 2 in 9 T at 4.2 K, indicating very weak field dependence. A nearly isotropy of Jc (γ= J H//ab c /J H//c c ) as low as 1.09 at 9 T is achieved in the FST thin films. Moreover, no clear amorphous interfacial layer presents between the film and the substrate probably ascribing to low temperature and low laser repetition rate grown, while the thickness of reaction layer is approximate 5 nm in many other works. The evidences of transmission electron microscopy show some lattices with lateral size of < 5 nm×20 nm seem to be disturbed. Those location defects are thought to be responsible for nearly isotropic behavior of superconductivity.

Similar to other high-temperature superconductors, the pinning centers largely determine the critical current density (Jc) in Co-doped BaFe2As2 (Ba122:Co). Therefore, understanding the vortex pinning mechanism of high-Jc Ba122:Co thin films is important for the applications of Ba122:Co. Herein we report the pinning of the naturally grown defects in Ba122:Co thin films with a high critical current density. The transport Jc of thin films is up to 2.6 MA cm−2 in 9 T at 4.2 K, which is the highest value in iron-based superconductors. Microstructure investigations reveal a high density of ab-planar defects (stacking faults) and localized vertical defects present in the sample. The Dew–Hughes mode analyses prove that pinning centers by surface defects and by point defects are responsible for H//ab and H//c, respectively. Therefore, the high Jc in strong magnetic field for both H//ab and H//c are related to surface and point defects which act as the pinning centers in Ba122:Co films.

We report on the transport properties of FeSe0.5Te0.5 (FST) thin films fabricated on less-well-textured flexible coated conductor templates with LaMnO3 (LMO) as buffer layers using pulsed laser deposition. The LMO buffer layers exhibit large in-plane misalignment of ∼7.72°, which is unfavorable for cuprate-coated conductors due to the high grain boundaries. The FST thin films show a superconducting transition temperature of 16.8 K, higher than that of bulk materials due to the compressive strain between LMO and FST. Atomic force microscopy observations reveal that island-like features appear at the surfaces of both LMO and FST, confirming the island growth mode. A self-field transport critical-current density of up to 0.43 MA cm−2 at 4.2 K has been observed in FST thin films, which is much higher than that in powder-in-tube processed FST tapes. The films are capable of carrying current densities  of over 105 A cm−2 in the whole applied magnetic field up to 9 T, showing great potential for high-field applications. The results indicate that, for FST, highly textured metal tapes are not needed to produce coated conductors with high performance, which is of great advantage over cuprate-coated conductors.