The XXZ Heisenberg spin chain H = Σ[JΔSᵢᶻSᵢ₊₁ᶻ + J(Sᵢˣ Sᵢ₊₁ˣ + Sᵢʸ Sᵢ₊₁ʸ)] is solved via exact diagonalization. The entanglement spectrum reveals the quantum phase structure through Schmidt values of the bipartition.
Entanglement entropy S = — | Ground state energy E₀ = —