A manifestation of the frustration effect in S=1/2 quantum spin systems

Abstract

The ground state properties of S=¹/₂ anisotropic Heisenberg magnets with plaquette frustration are investigated. The models can be classified according to whether a straightforward generalisation of the Marshall ansatz (1955) can be applied, or whether the ground state has to be approximated by a linear combination of Ising ground states. In the former case, the quantum ground state may have a zero-point entropy. In the latter case, a unique ground state with quantum liquid-like coherence properties is postulated, generalising an earlier suggestion by Fazekas and Anderson (1974).