Comparative study of the magnetoresistivity of YBa 2Cu 3O 7− δ and Bi 2Sr 2Ca Cu 2O 8+ x epitaxial thin films in the fluktuation regime

Abstract

We measured the magnetoresistivity of high quality, c-axis oriented epitaxial YBa 2Cu 3O 7− δ and Bi 2Sr 2Ca Cu 2O 8+ x (BSCCO) thin films in the fluctuation regime above the critical temperature. The measurements have been performed in magnetic fields up to 12 Tesla applied parallel and perpendicular to the CuO 2-planes. The experimental data was analysed in the framework of the Lawrence-Doniach model with the appropriate clean limit expressions for the Aslamazov-Larkin- and Maki-Thompson- fluctuation conductivities. Orbital as well as Zeeman contributions to the magnetoconductivity have been taken into account. With the thermodynamic critical temperature T c , the coherence lengths parallel and perpendicular to the ab-plane ξ ab and ξ c , respectively, and the product of the mean free path l and the phase breaking time τ φ as fitting parameters, good agreement between experiment and theory was found for YBCO, whereas for BSCCO no convincing fit could be obtained. Fitting the data for YBCO we obtained T c = 90.2 K, ξ ab = 13.8 A ̊ , ξ c = 3.1 A ̊ , and (lτ gf) 100 K ≅ 1.5 × 10 −22 sm . These values are close to those derived from measurements of the transport energy of magnetic flux lines via the Nernst effect at temperatures below T c . For BSCCO we obtained T c ≅ 90 K and ξ ab ≅ 24 to 30 Å. The very small coherence length in c-direction ξ c ≤ 0.4 Å reflects the quasi 2-dimensional nature of this material.