Comparison of the π and Δ operator approximations for the two-dimensional t-J model

We compare the spectra of the new π operator of the SO(5) theory and the conventional Δ operator for the two-dimensional t-J model. We also calculate the weight transferred to the two-hole ground state from half-filling by these operators. We find that the spectra of these operators are quite similar and the weight for the π operator is smaller than the weight for the Δ operator. We argue that the two-dimensional t-J model does not have a good approximate SO(S) symmetry claimed in Ref. [1]. © 1999 Published by Elsevier Science B.V. All rights reserved.