First-order spin-Peierls transition in S=1 antiferromagnetic Heisenberg chains Original Research Article

We investigate a one-dimensional S=1 antiferromagnetic Heisenberg model coupled to a lattice distortion by a quantum Monte Carlo method. The instability to a dimerized chain depends on the value of the spin–phonon coupling, unlike the case of S=1/2. We find the first-order transition between the uniform Haldane state and the dimerized state. Two non-magnetic states coexist in the chain and a domain-wall structure is observed. In the coexistent state, we find that the length of the uniform Haldane region shrinks, which causes an asymmetrical bond distortion in the dimerized region.