One- and two-hole states in the two-dimensional t-J model via series expansions

We study one- and two-hole properties of the t-J model at half-filling on the square lattice using series expansion methods at T=0. The dispersion curve for one-hole excitations is calculated and found to be qualitatively similar to that obtained by other methods, but the bandwidth for small t/J is some 20% larger than given previously. We also obtain the binding energy and dispersion relation for two-hole bound states. The lowest bound state as t/J increases is found to be first d wave, and then p wave, in accordance with predictions based upon the Kohn-Luttinger effect. We also carry out a similar study for the r-J(z) model. [S0163-1829(98)00647-X].