Projected BCS Wave Functions for Low Dimensional Frustrated Spin Systems

Original · EN

Twenty-five years after the first proposal, the question whether the ground state of a frustrated spin-half system is well described by a spin-liquid Resonating Valence Bond (RVB) wave function is still controversial. A physically transparent representation of a RVB state can be obtained in fermionic representation with a standard BCS-type pairing wave function, working in the subspace with fixed number of electrons and no double occupancies. In this work, we show that, using this variational wave function with a careful parameterization of the pairing function, it is possible to obtain an extremely accurate ansatz for the ground state of the Heisenberg antiferromagnet with next-nearest neighbors interactions (J₁-J₂ model) in the regime of strong frustration. Indeed, in the spin-half realization of this model, it is known that the combined effect of frustration and zero-point motion interferes with the mechanism of spontaneously broken symmetry, giving rise to a non-magnetic phase of purely quantum-mechanical nature (J₂/J₁≃ 0.5). This wave function is proposed to represent the generic spin-half RVB ground state in spin liquids.