Internal structure of fluctuating Cooper pairs

In order to obtain information about the internal structure of fluctuating Cooper pairs in the pseudogap state and below the transition temperature of high T c superconductors, we solve the Bethe-Salpeter equation for the two-electron propagator in order to calculate a “pair structure function” $g_{P}({\mathbf{P}},\pmb{\rho})$ that depends on the internal distance $\pmb{\rho}$ between the partners and on the center of mass momentum P of the pair. We use an attractive Hubbard model with a local potential for s-wave and a separable potential for d-wave symmetry. The amplitude of g P for small ρ depends on temperature, chemical potential and interaction symmetry, but the ρ dependence itself is rather insensitive to the interaction strength. Asymptotically g P decreases as an inverse power of ρ for weak coupling, but exponentially when a pseudogap develops for stronger interaction. Some possibilities of observing the pair structure experimentally are mentioned. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006