Superconductivity generated by coupling to a cooperon in a two-dimensional array of four-leg Hubbard ladders

Starting from an array of four-leg Hubbard ladders weakly doped away from half-filling and weakly coupled by interladder tunneling, we derive an effective low-energy model which contains a partially truncated Fermi surface and a well-defined cooperon excitation formed by a bound pair of holes. An attractive interaction in the Cooper channel is generated on the Fermi surface through virtual scattering into the cooperon state. Although the model is derived in the weak coupling limit of a four-leg ladder array, an examination of exact results on finite clusters for the strong coupling t-J model suggests the essential features are also present for a strong coupling Hubbard model on a square lattice near half-filling.