S=2 Quantum Spin Chain with the Biquadratic Exchange Interaction

TL;DR

This paper investigates the phase diagram of an S=2 quantum spin chain with biquadratic exchange and anisotropy, revealing a symmetry protected topological phase and a plateau phase at half saturation.

Contribution

It provides the first detailed numerical analysis of the S=2 chain with biquadratic interactions, identifying the SPT phase and its stability region.

Findings

Intermediate-D phase is an SPT phase in the phase diagram.

The SPT plateau phase exists at half saturation magnetization.

The phase diagram includes a wide region of the SPT phase.

Abstract

The $S=2$ quantum spin chain with the single-ion anisotropy $D$ and the biquadratic exchange interaction $J_{\rm BQ}$ is investigated using the numerical diagonalization of finite-size clusters and the level spectroscopy analysis. It is found that the intermediate-$D$ phase corresponding to the symmetry protected topological (SPT) phase appears in a wide region of the ground state phase diagram. We also obtain the phase diagram at the half of the saturation magnetization which includes the SPT plateau phase.