LINEAR SPIN-WAVES IN A FRUSTRATED HEISENBERG-MODEL

A Heisenberg model, which has the property that its classical ground state shows a continuous transition from the Néel to an incommensurate spiral state, is investigated. It is shown that even for arbitrarily large spin these states are not stable with respect to quantum spin fluctuations in a finite region of the parameter space. Outside this region the order of the classical ground state is not de- stroyed. Thus, the results of linear spin-wave theory suggest the existence of a quantum-spin-liquid state between the Néel and an ordered incommensurate spiral phase. © 1990 The American Physical Society.