\label{fig:plasmonics}Panel (a): Absorption cross section of a pair of sodium nanowires. The driving electric field is polarised 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})
