Artificially Engineered Nanostrain in Iron Chalcogenide Superconductor Thin Film for Enhancing Supercurrent

Although nanoscale deformation, such as nanostrain in iron chalcogenide (FeSexTe1-x, FST) thin films, has drawn attention due to the enhancement of general superconducting properties such as critical current density (Jc) and critical transition temperature, its formation has proven to be a very challenging and complex process thus far. Herein, we successfully fabricated an epitaxial multilayer FST thin film with uniformly distributed nanostrain via the injection of a trace of CeO2 between each FST layer using sequential pulsed laser deposition. Using transmission electron microscopy and geometrical phase analysis, we verified that a trace of CeO2 injection forms nanoscale fine defects with nanostrained region, which has a tensile strain ({\epsilon}_zz~0.05) for the c-axis of the FST matrix. The CeO2 injected FST thin film achieves a remarkable Jc of 3.6 MA/cm2 for a self-field and 90% enhanced Jc under 13 T with respect to a pristine FST thin film.