  We propose a new type of spatially periodic structure, i.e. polaritonic
crystal (PolC), to observe a "slow"/"stopped" light phenomenon due to coupled
atom-field states (polaritons) in a lattice. Under the tightbinding
approximation, such a system realizes an array of weakly coupled trapped
two-component atomic ensembles interacting with optical field in a
tunnel-coupled one dimensional cavity array. We have shown that the phase
transition to the superfluid Bardeen-Cooper-Schrieffer state, a so-called
(BCS)-type state of low branch polaritons, occurs under the strong coupling
condition. Such a transition results in the appearance of a macroscopic
polarization of the atomic medium at non-zero frequency. The principal result
is that the group velocity of polaritons depends essentially on the order
parameter of the system, i.e. on the average photon number in the cavity array.
