Theory of coherence lengths, fluctuation conductivity, and fluctuation specific heat in high- Tc oxide superconductors

Abstract

The fluctuation conductivity and specific heat are derived from the Aslamazov-Larkin theory by taking into account the quasi two-dimensionality of the effective tight-binding band. The resulting coherence lengths in the basal plane are calculated explicitly for the Hubbard models of Emery and Mattis and Mattis. They turn out to depend sensitively on band width, band filling, impurity scattering rate, and pair state ( s-wave, d-wave, and uniaxial s- d-wave). Small band dispersion along the c-axis yields 2D to 3D crossover as T → T c . Our theory is capable of accounting for the small coherence lengths derived from measurements of H c2 , the fluctuation conductivity, and the specific heat in YBa 2Cu 3O 7. We suggest measurements of the fluctuation conductivity at microwave or infrared frequencies.