Valence-bond spin-liquid state in two-dimensional frustrated spin-1/2 Heisenberg antiferromagnets

Fermionic valence-bond approach in terms of SU(4) representation is proposed to describe the J(1)-J(2) frustrated Heisenberg antiferromagnetic (AF) model on a bipartite square lattice. A uniform mean field solution without breaking the translational and rotational symmetries describes a valence-bond spin-liquid state, interpolating the two different AF ordered states in the large J(1) and large J(2) limits, respectively. This novel spin-liquid state is gapless with the vanishing density of states at the Fermi nodal points. Moreover, a sharp resonance peak in the dynamic structure factor is predicted for momenta q=(0,0) and (pi,pi) in the strongly frustrated limit J(2)/J(1)similar to1/2, which can be checked by neutron scattering experiments.