Medium effects on the van der Waals force

M. S. Tomaš

Ruđer Bošković Institute, P. O. B. 180, 10002 Zagreb, Croatia

Email: tomas@thphys.irb.hr

Although it is known for quite some time that the surrounding medium [1] and the presence of nearby boundaries [2] have strong effects on the van der Waals (atom-atom) interaction, considerations of the combined medium and boundary effects in realistic systems on it appeared only recently [3,4]. In this work, we consider the medium effects on the van der Waals interaction potential (force) between two ground-state atoms embedded in adjacent semi-infinite magnetodielectric media. In this case, in addition of being screened by the surrounding media in a way similar to that of the van der Waals force in a single medium [5], the force is further reduced and becomes anisotropic owing to the transmission/refraction of the vacuum field across the interface. We also calculate the Casimir-Polder force on an atom A arising from the uniform distribution of the atoms B in the medium across the interface. Comparison of this force with the corresponding result deduced from the Casimir force on a thin slab in front of a composite medium obeying the Clausius-Mossotti relation, suggests a hint on how to improve a well-known formula for the van der Waals potential [2,3,4] with respect to the local-field effects.

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