D-WAVE BOUND-STATE OF HOLES IN AN ANTIFERROMAGNET

The formation of bound states of holes in an antiferromagnetic spin-1/2 background is studied using numerical techniques applied to the t-J Hamiltonian on clusters with up to 26 sites. An analysis of the binding energy as a function of cluster size suggests that a two-hole bound state is formed for couplings larger than a ''critical'' value J\t\c. The symmetry of the bound state is d(x2-y2). We also observed that its ''quasiparticle'' weight Z2h (defined in the text), is finite for coupling J/t greater-than-or-equal-to J\t\c. Thus, in the region J/t greater-than-or-equal-to J/t/c the bound state of two holes behaves like a quasiparticle with charge Q - 2e, spin S = 0, and d(x2-y2) internal symmetry. The relation with recent ideas that have suggested the possibility of d-wave pairing in theories of the high-T(c) cuprates is briefly discussed.