Application of the Lifshitz theory to poor conductors

The Lifshitz formula for the dispersive forces is generalized to the materials, which cannot be described with the local dielectric response. Principal nonlocality of poor conductors is related with the finite screening length of the penetrating field and the collisional relaxation; at low temperatures the role of collisions plays the Landau damping. The spatial dispersion makes the theory self consistent. Our predictions are compared with the recent experiment. It is demonstrated that at low temperatures the Casimir-Lifshitz entropy disappears as $T$ in the case of degenerate plasma and as $T^2$ for the nondegenerate one.