Spin correlations and Haldane gap in the S = 2 antiferromagnetic Heisenberg chain

Abstract

Haldane's conjecture for the S = 2 antiferromagnetic Heisenberg chain is investigated with a quantum Monte Carlro method. The ground-state spin-spin correlation function and an excitation gap immediately above the ground state are calculated for chains up to 512 spins. The large-separation correlations are well fitted to the two-dimensional Ornstein-Zernike form. The correlation length and the Haldane gap in the unit of the exchange constant are estimated to be 61 −6 +8 and 0.074 ± 0.016, respectively.