Pairfield fluctuations in the 2D Hubbard Model*

The nature of the pseudogap phase out of which superconductivity emerges in the cuprates remains an open problem. Pairfield fluctuations above the superconducting transition temperature provide information on the nature of this phase. Here we report numerical calculations of the d-wave pairfield susceptibility of a 2D Hubbard model for dopings which have a pseudogap and for dopings which do not. One knows that in both cases there will be a region of Kosterlitz-Thouless fluctuations as the transition at T_KT is approached. Above this region, we find evidence that the pseudogap limits the growth of the local pairfield and provides an environment in which phase fluctuations determine the temperature dependence of the pairfield susceptibility. In contrast, in the overdoped regime where there is no pseudogap, the temperature dependence of the pairfield is consistent with Ginzburg-Landau amplitude fluctuations. We discuss an experiment that can be used to measure this characteristic difference.