J1-J2 quantum Heisenberg antiferromagnet: improved spin-wave theories versus exact-diagonalization data

Abstract

We reconsider the results concerning the extreme-quantum S=1/2 square-lattice Heisenberg antiferromagnet with frustrating diagonal couplings (the J1-J2 model) drawn from a comparison with exact-diagonalization data. A combined approach, also using some intrinsic features of the self-consistent spin-wave theory, leads to the conclusion that the theory strongly overestimates the stabilizing role of quantum fluctuations with respect to the Neel phase in the extreme-quantum case S=1/2. On the other hand, the analysis implies that the Neel phase remains stable at least up to the limit J2/J1=0.49, which is larger than some previous estimates. In addition, it is argued that the spin-wave ansatz predicts the existence of a finite range (J2/J1<0.323 in linear spin-wave theory) where the Marshan-Peierls sign rule survives the frustrations,.