Phase diagram of the frustrated square Heisenberg lattice based upon a modified spin-wave theory

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Abstract
We show that the conventional spin-wave theory cannot give a correct phase diagram for the frustrated square-lattice antiferromagnet. We present a modified spin-wave theory for this model, which is analogous to Takahashi’s recent theory of the two-dimensional Heisenberg model without frustrations, and obtain a new phase diagram in which there exists no spin-liquid state for S=1/2. Our results agree well with those of recent numerical simulations for small lattices.