HOLE BINDING IN THE T-J MODEL

We calculated the binding energy of two holes with antiparallel spin i n the t-J model using a variational wave function based on the string or spin-bag picture. The symmetry of the bound state is d(x)2-(y)2. Al though the size of matrices to be diagonalized is only 3 x 3 we could reproduce the results of various extensive numerical calculations with reasonable accuracy. We show that a sizeable contribution of the bind ing energy is due to the quantum fluctuations in the ground state of t he Heisenberg antiferromagnet. In contrast to exact diagonalization re sults on small clusters in the thermodynamical limit the binding energ y decreases rapidly with increasing t/J. A detailed discussion of the various finite-size effects in a small cluster is also included.