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

We study oneand two-hole properties of the t-J model at half-filling on the square lattice using series expansion methods at T50. 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 t-Jz model. @S0163-1829~98!00647-X#