SELF-CONSISTENT SPIN-WAVE APPROACH TO THE SPIN-1/2 FRUSTRATED HEISENBERG-MODEL

The spin-1/2 Heisenberg antiferromagnet with the nearest neighbor interaction J1 and the next nearest neighbor one J2 is studied on the square lattice by use of the self-consistent spin-wave approach, in which an on-site exclusion principle, i.e., (Sj(y))2 +(S(j)z)2=1/2 with the x-axis taken as a quantized one is satisfied at any lattice point j on the average. From this constraint, the zero-temperature long-range order sigma0 and ground-state energy E0 are determined as a function of alpha=J2/J1. The behaviors of sigma0, and E0 near alpha=0.5 are very different from the ones of the ordinary spin-wave theory based on the Holstein-Primakoff transformation. For example, our calculation predicts the vanishing long-range order at alpha=0.5. It is emphasized that the on-site exclusion principle fairly well suppresses the quantum spin fluctuations highly enhanced by the frustration.