NOVEL-APPROACH FOR THE ANALYSIS OF THE FLUCTUATION MAGNETOCONDUCTIVITY IN YBA2CU3O7 THIN-FILMS

We report measurements of the paraconductivity and of the fluctuation magnetoconductivity as a function of both the magnetic field up to 13 T and the temperature in thin epitaxial films of YBa2Cu3O7. An analysi s within the model for dirty-limit superconductors yields consistent v alues for the in-plane, the out-of-plane coherence lengths, and the qu asiparticle phase coherence time. Although an estimation of the mean f ree carrier path indicates that YBa2Cu3O7 is a clean superconductor, t he appropriate clean-limit theory produces an unrealisticly short phas e coherence time, around half the value of the transport scattering ti me, and fails to fit the paraconductivity data. We show that if the ma gnetoconductivity due to the orbital motion of the normal-state quasip articles is taken into account, the Maki-Thompson fluctuation contribu tion at high temperatures is significantly smaller than predicted by b oth clean- and dirty-limit theories. This result suggests non-s-wave p airing in YBa2Cu3O7.