Exact ground states of quantum spin-2 models on the hexagonal lattice

TL;DR

This paper constructs exact ground states for spin-2 quantum antiferromagnets on a hexagonal lattice, revealing different magnetic orders and potential quantum phase transitions, advancing understanding of complex quantum spin systems.

Contribution

It introduces a method to find exact non-trivial ground states of spin-2 models with realistic symmetries, including states with magnetic order and weak degeneracy.

Findings

Exact ground states with magnetic order identified

Weak degeneracy of the constructed states

Evidence of quantum phase transition within the model

Abstract

We construct exact non-trivial ground states of spin-2 quantum antiferromagnets on the hexagonal lattice. Using the optimum ground state approach we determine the ground state in different subspaces of a general spin-2 Hamiltonian consistent with some realistic symmetries. These states, which are not of simple product form, depend on two free parameters and can be shown to be only weakly degenerate. We find ground states with different types of magnetic order, i.e. a weak antiferromagnet with finite sublattice magnetization and a weak ferromagnet with ferrimagnetic order. For the latter it is argued that a quantum phase transition occurs within the solvable subspace.