Composite Metal-Semiconductor Metamaterials with Negative Permittivity and No Loss

Close to the resonance in a planar interface between a metal and dielectric, where $\varepsilon _{metal} \quad \approx -\varepsilon _{dielectric}$, very tight electromagnetic field confinement results, but the tighter the confinement, invariably, the higher the propagation losses. For confinement significantly better than that of Si nanowires ($\sim $300 nm) propagation losses become prohibitively high for most interconnect applications. Also, the magnitude of $\varepsilon _{metal}$ needs to be larger than e.g. 2 in order to interface to common dielectrics for close to resonance conditions. The most straightforward way to alleviate this situation is of course to use optical gain. We have analyzed theoretically a metamaterial, which is a mix of quantum dots (QDs) half of them pumped and half absorptive and showed that one could indeed compensate the loss. More efficient way of obtaining the $\varepsilon $'$<$0 is to use metals, and we show that a combination of silver rods, supplying the negative $\varepsilon $ and pumped QDs, providing the gain necessary to compensate the loss in the silver rods [1]. \\[3pt] [1] A. Bratkovsky, E. Ponizovskaya, S-Y. Wang, P. Holmstr\"{o}m, L. Thyl\'{e}n, Y. Fu, and H. {\AA}gren, Appl. Phys. Lett. \textbf{93}, 193106 (2008)