Mobile holes in a two-dimensional Heisenberg antiferromagnet

Th t-t'-t''-J model is investigated by a rigorous diagonalization in a two-dimensional square lattice as large as {}20 ×{} {}20 , which has no additional degeneracy. The ground state of one hole in the t-J model is at a momentum k near (±{}{π}/2,±{}{π}/2) with a total spin S=1/2 and that of two holes is at k=(0,0) with S=0. The hole pairing and nonclustering may be preferable for the ground state of the t-t'-t''-J model in the region of t'>0 and t''{}0.