G. Bouzerar et al., ELEMENTARY EXCITATIONS IN DIMERIZED AND FRUSTRATED HEISENBERG-CHAINS, Physical review. B, Condensed matter, 58(6), 1998, pp. 3117-3123
We present a detailed numerical analysis of the low-energy excitation
spectrum of a frustrated and dimerized spin S=1/2 Heisenberg chain. In
particular, we show that in the commensurate spin-Peierls phase the r
atio of the singlet and triplet excitation gap is a universal function
which depends on the frustration parameter only. We identify the cond
itions for which a second elementary triplet branch in the excitation
spectrum splits from the continuum. We compare our results with predic
tions from the continuum limit field theory. We discuss the relevance
of our data in connection with recent experiments on CuGeO3, NaV2O5, a
nd (VO)(2)P2O7.