Enhanced dispersion interaction between quasi-one-dimensional conducting collinear structures

Recent investigations have highlighted the failure of a sum of R-6 terms to represent the dispersion interaction in parallel metallic, anisotropic, linear, or planar nanostructures [J. F. Dobson, A. White, and A. Rubio, Phys. Rev. Lett. 96, 073201 (2006), and references therein]. By applying a simple coupled-plasmon approach and using electron hydrodynamics, we numerically evaluate the dispersion (noncontact van der Waals) interaction between two conducting wires in a collinear pointing configuration. This case is compared to that of two insulating wires in an identical geometry, where the dispersion interaction is modeled both within a pairwise summation framework and by adding a pinning potential to our theory leading to a standard oscillator-type model of insulating dielectric behavior. Our results provide a further example of enhanced dispersion interaction between two conducting nanosystems compared to the case of two insulating ones. Unlike our previous work, this calculation explores a region of relatively close coupling where, although the electronic clouds do not overlap, we are still far from the asymptotic region where a single power law describes the dispersion energy. We find that strong differences in dispersion attraction between metallic and semiconducting or insulating cases persist into this nonasymptotic region. While our theory will need to be supplemented with additional short-ranged terms when the electronic clouds overlap, it does not suffer from the short-distance divergence exhibited by purely asymptotic theories and gives a natural saturation of the dispersion energy as the wires come into contact.