Critical current density and vortex pinning mechanism of Lix(NH3)yFe2Te1.2Se0.8 single crystals

We grew Lix(NH3)yFe2Te1.2Se0.8 single crystals successfully using the low-temperature ammonothermal method and the onset superconducting transition temperature Tc,onset is increased to 21 K when compared to 14 K in the parent compound FeTe0.6Se0.4. The derived critical current density Jc increases remarkably to 2.6*10^5 A/cm^2 at 2 K. Further analysis indicates that the dominant pinning mechanism in Lix(NH3)yFe2Te1.2Se0.8 single crystal is the interaction between vortex and surface-like defects with normal core, possibly originating from the stacking faults along the c axis, by variations in the charge-carrier mean free path l near the defects (delta l pinning). Moreover, the flux creep is important to the vortex dynamics of this material.