Quenching of the Haldane gap in LiVSi2O6 and related compoundsB. Pedrini, S. Wessel, J. L. Gavilano, H. R. Ott, S. M. Kazakov and J. KarpinskiEur. Phys. J. B, 55 3 (2007) 219-228DOI: https://doi.org/10.1140/epjb/e2007-00056-0