Quantum lattice fluctuations as a source of frustration in the antiferromagnetic Heisenberg model on a square lattice

Abstract

A new approach has been developed to study the effect of quantum lattice fluctuations as a source of frustration in the antiferromagnetic Heisenberg model on a square lattice. By considering both the dispersional and dispersionless phonons we show that when the spin-phonon coupling constant α 2 2K or the phonon frequency ω ph increases the sublattice magnetization 〈 S A 2〉 decreases gradually. At some critical value ( α 2 2K ) c or ( ω ph) c, 〈 S A 2〉=0 and the long-range order disappears. This can be attributed to the fact that the ground state fails to develop the antiferromagnetic long-range order because of the quantum lattice fluctuations and some kind of quantum spin liquid state might be energetically favorable.