DIMENSIONALITY AND KOSTERLITZ-THOULESS TRANSITION IN SINGLE GRAIN TL-2223 SUPERCONDUCTING THIN-FILMS

Tl2Ba2Ca2Cu3O10+x (Tl-2223) superconducting films with microstructure consisted of submillimeter size grains combining with reactive ion etc hing technique, has enabled us to investigate the transport properties of this material in a more controllable manner. Both conductivity flu ctuations based on the Aslamazov-Larkin theory and the Kosterlitz-Thou less transitions were studied to delineate the two dimensional nature of the material. It was found that, depending on the substrate used, t he effective thickness of critical fluctuation and the detailed featur es of the K-T transition were very different. For films deposited on L aAlO3(100) substrates, the effective thickness of critical fluctuation is about 35 Angstrom compared to a value of 17.5 Angstrom obtained fo r films deposited on MgO(100) substrate, roughly equal to the c-axis l attice constant and the distance between the trilayer CuO2 planes, res pectively. The effective vortex dielectric constant measuring the corr elations 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 mec hanisms based on the defect structures are proposed to account for the observed results.