Dispersion interaction between crossed conducting wires

Abstract

We compute the $T=0\text{ }\text{K}$ Van der Waals (nonretarded Casimir) interaction energy $E$ between two infinitely long, crossed conducting wires separated by a minimum distance $D$ much greater than their radius. We find that, up to a logarithmic correction factor, $E\ensuremath{\propto}\ensuremath{-}{D}^{\ensuremath{-}1}{|\text{sin}\text{ }\ensuremath{\theta}|}^{\ensuremath{-}1}f(\ensuremath{\theta})$, where $f(\ensuremath{\theta})$ is a smooth bounded function of the angle $\ensuremath{\theta}$ between the wires. We recover a conventional result of the form $E\ensuremath{\propto}\ensuremath{-}{D}^{\ensuremath{-}4}{|\text{sin}\text{ }\ensuremath{\theta}|}^{\ensuremath{-}1}g(\ensuremath{\theta})$ when we include an electronic energy gap in our calculation. Our prediction of gap-dependent energetics may be observable experimentally for carbon nanotubes either via atomic force microscopy detection of the Van der Waals force or torque or indirectly via observation of mechanical oscillations. This shows that strictly parallel wires, as assumed in previous predictions, are not needed to see a unique effect of this type.