We study the properties of one-dimensional photonic crystals with an $\epsilon$-negative and a $\mu$-negative defect. With suitable parameters, the pair defect is equivalent to a transparent material with zero effective refractive index. This special pair defect has no influence on the spectral gap formed by the interference of propagating waves in positive-refractive-index materials. However, the field distribution is modified noticeably by the decaying wave in the pair defect. Particularly, the gap-edge field can be a highly localized wave instead of the usual standing wave as the size of the pair defect increases. The localized gap-edge field can reduce the switching thresholds for bistability greatly when Kerr-type nonlinear $\mu$-negative material is involved. A nonideal model when the $\epsilon$-negative and $\mu$-negative materials are dispersive and lossy is used to verify the unusual properties.

• Received 21 December 2005

DOI:https://doi.org/10.1103/PhysRevE.73.046601