Nonclassical disordered phase in the strong quantum limit of frustrated antiferromagnets

The rotationally invariant Schwinger-boson approach to quantum helimagnets is discussed. It is shown that in order to get quantitative agreement with exact results on finite lattices, parity-breaking pairing of bosons must be allowed. For the ${\mathit{J}}_1$-${\mathit{J}}_2$-${\mathit{J}}_3$ model on the special line ${\mathit{J}}_2$=2${\mathit{J}}_3$, a quantum disordered phase is found, though notably only in the strong quantum limit S=1/2. The theory predicts the direct melting of biaxial helimagnetic order into an isotropic spin fluid, without the formation of an intermediate spin-nematic phase as recently suggested.