Gap function ϕ (k,ω) for a two-leg t-J ladder and the pairing interaction

The gap function ϕ(k,ω) , 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 the order of the bandwidth.