Coherence length in deoxygenated (1 0 3)/(0 1 3) oriented YBCO superconductor films

Abstract

The coherence length ξ c along c-axis direction in (1 0 3)/(0 1 3) oriented YBCO superconductor thin films has been evaluated from the temperature dependence of current–voltage ( I– V) characteristics of micro-bridges in the framework of a model taking in account thermally activated magnetic flux creep in the intrinsic potential of the layered structure of the superconductor. The coherence length gradually increased from the initial value ξ c = 0.14 nm to ξ c = 0.33 nm in the sample subjected to subsequent annealing steps performed in air at increasing temperatures from a range T a = 190–275 °C. Structural modifications of deoxygenated samples were monitored by micro-Raman spectroscopy. The critical temperature T c slightly increases after the initial annealing steps while a significant T c decrease has been observed after T a = 275 °C stage accompanied by appearance of the tetragonal phase in the crystal structure.