Soliton approach to spin-Peierls antiferromagnets: Large-scale numerical results

A simple intuitive picture of spin-Peierls antiferromagnets arises from regarding the elementary excitations as S=1/2 solitons. We investigate these excitations numerically in a phononless model where spontaneous dimerization arises from frustration and the interchain coupling is treated in mean field theory. It is shown that in a strictly one-dimensional system without any explicit dimerization, soliton-antisoliton bound-states do not form and the solitons are repelled by impurities. Couplings to the three-dimensional lattice produce an effective confining potential and we show that in this case solitons bind to antisolitons and to impurities, with the number of such bound-states increasing as the interchain coupling goes to 0.