Connectivity transition in the frustrated S=1 chain revisited -: art. no. 100401

The phase transition in the antiferromagnetic isotropic Heisenberg S=1 chain with frustrating next-nearest-neighbor coupling alpha is reconsidered. We identify the order parameter of the large-alpha phase as describing two intertwined strings, each possessing a usual string order. The transition has a topological nature determined by the change in the string connectivity. Numerical evidence from the density matrix renormalization group results is supported by the effective theory based on soliton states.