\label{fig:FIGURE_plasmonics} Panel (a): Absorption cross section of a pair of sodium nanowires. The driving electric field is polarized as shown in the inset. Curves are for different values of gap, $d$, between the nanowires, From top to bottom: $d=5,\ 2,\ 1,\ 0.5,\ 0.2,\ 0.1,\ 0$ nm. 
Panel (b): Field enhancement, $h$, for the case $d=0.5$ nm. The black lines indicate the nanowire surfaces. (Adapted from Ref.~\cite{Stella_2013})