Interaction energy between a positronium atom and a metal surface

Abstract

The interaction energy of a positronium atom interacting with a metal surface is obtained as a function of the speed of the positronium atom and the separation from the metal surface. It is shown that the energy saturates to a finite value at the surface and follows the Lifshitz relation for large separations. The treatment is based on the consideration of the virtual excitations of the multipoles of the atom, while in the earlier work by Manson and Ritchie only the dipolar excitations were considered. The divergence of the interaction energy obtained by the earlier authors arises due to incomplete consideration of multipolar effects.