The Gap Function Phi(k,w) for a Two-leg t-J Ladder and the Pairing   Interaction
  The gap function phi(k,omega), determined from a Lanczos calculation for a doped 2-leg t-J ladder, is used to provide insight into the spatial and temporal structure of the pairing interaction. It implies that this interaction is a local near-neighbor coupling which is retarded. The onset frequency of the interaction is set by the energy of an S=1 magnon-hole-pair and it is spread out over a frequency region of order the bandwith. 
Didier Poilblanc (LPT), Douglas J. Scalapino