Competition between two- and three-sublattice ordering for S=1 spins on the square lattice

TL;DR

This paper demonstrates that quantum fluctuations induce an extended three-sublattice phase in the S=1 bilinear-biquadratic Heisenberg model on a square lattice, challenging classical expectations and revealing complex quadrupolar ordering.

Contribution

It provides evidence for a quantum fluctuation-induced three-sublattice phase in a bipartite lattice, using exact diagonalizations and semiclassical flavor-wave theory.

Findings

Identification of a three-sublattice phase induced by quantum fluctuations.

The phase is purely quadrupolar in zero field.

The phase replaces the 1/2 plateau at higher fields.

Abstract

We provide strong evidence that the S=1 bilinear-biquadratic Heisenberg model with nearest-neighbor interactions on the square lattice possesses an extended three-sublattice phase induced by quantum fluctuations for sufficiently large biquadratic interactions, in spite of the bipartite nature of the lattice. The argumentation relies on exact diagonalizations of finite clusters and on a semiclassical treatment of quantum fluctuations within linear flavor-wave theory. In zero field, this three-sublattice phase is purely quadrupolar, and upon increasing the field it replaces most of the plateau at 1/2 that is predicted by the classical theory.