Point defect induced giant enhancement of flux pinning in Co-doped FeSe0.5Te0.5 superconducting single crystals

Point defect pinning centers are the key factors responsible for the flux pinning and critical current density in type II superconductors. The introduction of the point defects and increasing their density without any changes to the superconducting transition temperature Tc, irreversibility field Hirr, and upper critical field Hc2, would be ideal to gain insight into the intrinsic point-defect-induced pinning mechanism. In this work, we present our investigations on the critical current density Jc, Hc2, Hirr, the activation energy U0, and the flux pinning mechanism in Fe1-xCoxSe0.5Te0.5 (x = 0, 0.03 and 0.05) single crystals. Remarkably, we observe that the Jc and U0 are significantly enhanced by up to 12 times and 4 times for the 3at.% Co-doped sample, whereas, there is little change in Tc, Hirr, and Hc2. Furthermore, charge-carrier mean free path fluctuation, δl pinning, is responsible for the pinning mechanism in Fe1-xCoxSe0.5Te0.5.