Magnetic order and ballistic spin transport in a sine-Gordon spin chain

We report the results of muon-spin spectroscopy (mu+SR) measurements on the staggered molecular spin chain [pym-Cu(NO3)(2)(H2O)(2)] (pym = pyrimidine), a material previously described using sine-Gordon field theory. Zero-field mu+SR reveals a long range magnetically ordered ground state below a transition temperature T-N = 0.23(1) K. Using longitudinal-field (LF) mu+SR we investigate the dynamic response in applied magnetic fields 0 < B < 500 mT and find evidence for ballistic spin transport. Our LF mu+SR measurements on the chiral spin chain [Cu(pym)(H2O)(4)]SiF6 center dot H2O instead demonstrate one-dimensional spin diffusion, and the distinct spin transport in these two systems suggests that additional anisotropic interactions play an important role in determining the nature of spin transport in S = 1/2 antiferromagnetic chains.