Mimicking Boyer's Casimir repulsion with a nanowire material

It is shown that the electromagnetic Casimir force acting on a conducting body (e. g., a realistic metallic piston) sliding in a background formed by cut silver nanorods (with the body perforated by the nanorods) is repulsive at distances larger than the separation of the nanorods, even if the host material of the nanorods is air. It is demonstrated that the physical origin of this effect is in essence related to Boyer's prediction that magnetic and conducting walls repel each other. Indeed, we show that from the point of view of an observer inside the nanowire structure, the interface formed by severing the nanowires mimics accurately the behavior of a magnetic wall for P-polarized waves. In contrast to other piston configurations reported in the literature, the Casimir interaction in the nanowire background is an ultralong-range force that decays with the distance to the nearby interface as 1/a(2).