Entanglement in the quantum one-dimensional integer spin S Heisenberg antiferromagnet

We use the modified spin wave theory of Takahashi to study the entanglement entropy in the quantum one-dimensional integer spin Heisenberg antiferromagnet. We calculate the entanglement entropy of this spin system that is well known to be a quantum wire, in the classical limit (N→∞). We obtain a decreasing the entanglement entropy with the temperature and we obtain none change in the entanglement in the point Δ=1 at T=0 where the system presents a quantum phase transition from a gapless phase in the spectrum Δ<1 to a gapped phase Δ≥1.