Dimensionality and kosterlitz-thouless transition in single grain Tl-2223 superconducting thin films

Tl₂Ba₂Ca₂Cu₃O_10+x (Tl-2223) superconducting films with microstructure consisted of submillimeter size grains combining with reactive ion etching technique, has enabled us to investigate the transport properties of this material in a more controllable manner. Both conductivity fluctuations based on the Aslamazov-Larkin theory and the Kosterlitz-Thouless transitions were studied to delineate the two dimensional nature of the material. It was found that, depending on the substrate used, the effective thickness of critical fluctuation and the detailed features of the K-T transition were very different. For films deposited on LaAlO₃(100) substrates, the effective thickness of critical fluctuation is about 35 Åcompared to a value of 17.5 Åobtained for films deposited on MgO(100) substrates, roughly equal to the c-axis lattice constant and the distance between the trilayer CuO₂ planes, respectively. The effective vortex dielectric constant measuring the correlations between vortex pairs near K-T transition were estimated to be 3.0 and 1.6 for films on LaAlO₃ and on MgO, repectively. Possible mechanisms based on the defect structures are proposed to account for the observed results.