Effectively left-handed (negative index) composite material

We show that a layered material, with alternating layers having negative permittivity (ε<0) and negative permeability (μ<0), responds to electromagnetic fields in many ways like a homogeneous left-handed material with ε<0 and μ<0. In particular, such a layered structure supports electromagnetic waves with group velocity antiparallel to the phase velocity. However, phase-sensitive measurements of the scattering matrix would distinguish the material from a homogeneous left-handed material. The appearance of a mode with positive index of refraction (right-handed mode) at frequencies for which ε and μ are negative is a surprising feature.