Experimental investigation on zero-Øeff gaps of photonic crystals containing single-negative materials Liwei Zhang, Yewen Zhang, Li He, Hongqing Li and Hong Chen Eur. Phys. J. B, 62 1 (2008) 1-6 Published online: 19 March 2008 DOI: 10.1140/epjb/e2008-00116-y