Possible spin-liquid state at largeSfor the frustrated square Heisenberg lattice

We present conventional spin-wave calculations for a frustrated antiferromagnetic Hamiltonian on a square lattice. We find that quantum fluctuations can destabilize the classical ordered ground state, even at large S, for large enough values of frustration. This instability is likely to generate a spin liquid, providing the first example of a resonating-valence-bond ground state in two dimensions.