Atom-atom interactions at and between metal surfaces at nonzero temperature

We have investigated the temperature-dependent Casimir-Polder interaction between two oscillators in the proximity of metal surfaces. The interaction near a single metal surface has much in common with the interaction in free space. However, at any finite temperature the long-range asymptote is equal to the hightemperature asymptote. This asymptote, which originates not from the n50 term in the Matsubara summation but from thermal population of the n.0 terms, is F(R)522kBTa0 /R6. This should be compared with the more rapidly decaying zero-temperature Casimir-Polder asymptote, F(R)'213\ca0 /(2pR7). The interaction in the midplane between two metallic surfaces is very different. The nonretarded interaction decreases exponentially and the interaction is dominated by an enhanced Casimir-Polder-like asymptote. At large separations this asymptote also decays exponentially. For any relevant temperatures the long-range asymptote is no longer equal to the high-temperature limit. In other words crossover to a classical limit found for the longrange interaction in free space, and on a metal surface, is not always valid in a narrow cavity.