Exact ground states of spin-2 chains

TL;DR

This paper constructs exact ground states for anisotropic spin-2 chains using matrix product states, revealing multiple magnetic phases and providing insights into higher-spin chain behaviors.

Contribution

It introduces a method to explicitly construct all ground states of spin-2 chains with symmetries, identifying various magnetic phases and their properties.

Findings

Identification of three antiferromagnetic Haldane phases

Discovery of weak antiferromagnetic and ferromagnetic phases

Description of antiferromagnetic phases as spin liquids with exponential decay

Abstract

We use the matrix product approach to construct all optimum ground states of general anisotropic spin-2 chains with nearest neighbour interactions and common symmetries. These states are exact ground states of the model and their properties depend on up to three parameters. We find three different antiferromagnetic Haldane phases, one weak antiferromagnetic and one weak ferromagnetic phase. The antiferromagnetic phases can be described as spin liquids with exponentially decaying correlation functions. The variety of phases found with the matrix product ansatz also gives insight into the behaviour of spin chains with arbitrary higher spins.