Hole-hole effective interaction in the two-dimensional Hubbard model

We present the first exact results of the ground-state energy in the two-dimensional Hubbard model on a 4×4 cluster for several values of U and fillings. The behavior of the binding energy of two holes as a function of U is discussed together with some analytical results in limiting cases. The analysis of the hole-hole correlation function allows one to determine the range of values of U where binding might be seen. © 1990 The American Physical Society