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High performance FeSe0.5Te0.5 thin films grown at low temperature by pulsed laser deposition

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/cm2 in self-field and 0.97 MA/cm2 in 9 T at 4.2 K, indicating very weak field dependence. A nearly isotropy of Jc (γ= Jc(H//ab)/Jc(H//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 x 20 nm seem to be disturbed. Those location defects are thought to be responsible for nearly isotropic behavior of superconductivity.