1. Enhanced van der Waals interaction at interfaces Marin-Slobodan Tomaš Ruđer Bošković Institute, Zagreb, Croatia

2. Introduction Consider an excited (e) atom A and a ground-state (g) atom B in an inhomogeneous system, e.g., near a body. A B

3. Assuming two-level isotropic atoms the vacuum force on the atom A is obtained from the potential Wylie and Sipe (1985) [G. S. Agarwal (1974)] Y. Sherkunov (2007)

4. Assuming two-level isotropic atoms the vacuum force on the atom A is obtained from the potential Wylie and Sipe (1985) [G. S. Agarwal (1974)] Y. Sherkunov (2007)

5. Now, near a surface (resonant) mode frequency Accordingly R. R. Chance et al. (1975) H. Failache et al. (1999)

6. System

7. Green function For z A +z B  1, the Green function reads Note that

8. Resonant two-atom potential enhancement factor { normalization unit

9. Model calculation Assuming atoms in the vacuum near a Lorentz type medium we have [Barton (1997)]

10. It is immediately seen that at resonance  A =  S Since for insulators  /  S ~ 10 -2 and for (noble) metals  /  S ~ 10 -3, this implies that under circumstances of the resonant coupling of the atom A to the surface polariton mode at nearby surface the van der Waals (two-atom) potential can be enhanced with respect to its free-space value by several orders of magnitudes. Estimate

11. Results for the sapphire surface || g   S )=299.2 g   S )=113.7 [ε(∞)=2.71, ε(0)=6.57,  S =1.54x10 14 s -1,  S ]

12.  B =0.9  S  B =1.1  S ||

13. Double resonance B=SB=S

14. Conclusion - The (generalized) Sherkunov formula implies a strong enhancement of the van der Waals (atom*-atom) interaction near an interface under the circumstances of the resonant coupling of the excited atom with the surface polariton mode of the system. It is very likely that the same holds for the retarded atom*-atom interaction where, owing to the dispersion of the surface polariton mode, the atom*-surface resonance can be obtained much easier. This promotes the van der Waals interaction as another example of the surface enhanced phenomena. and a guess