From gapped excitons to gapless triplons in one dimension Mohsen Hafez-Torbati, Nils A. Drescher and Götz S. Uhrig Eur. Phys. J. B, 88 2 (2015) 36 Published online: 02 February 2015 DOI: 10.1140/epjb/e2014-50551-0