String order and degenerate entanglement spectrum of S = 1 / 2 and S = 1 Heisenberg bond-alternating chainsXiao-Yan Deng, Long-Juan Kong and Ling QiangEur. Phys. J. B, 87 10 (2014) 247DOI: https://doi.org/10.1140/epjb/e2014-50391-x