Photo-induced electron transfer in the strong coupling regime: Waveguide-plasmon polaritons

Reversible exchange of photons between a material and an optical cavity can lead to the formation of hybrid light--matter states where material properties such as the work function\cite{Hutchison_AM2013a}, chemical reactivity\cite{Hutchison_ACIE2012a}, ultra--fast energy relaxation \cite{Salomon_ACIE2009a,Gomez_TJOPCB2012a} and electrical conductivity\cite{Orgiu_NM2015a} of matter differ significantly to those of the same material in the absence of strong interactions with the electromagnetic fields. Here we show that strong light--matter coupling between confined photons on a semiconductor waveguide and localised plasmon resonances on metal nanowires modifies the efficiency of the photo--induced charge--transfer rate of plasmonic derived (hot) electrons into accepting states in the semiconductor material. Ultra--fast spectroscopy measurements reveal a strong correlation between the amplitude of the transient signals, attributed to electrons residing in the semiconductor, and the hybridization of waveguide and plasmon excitations.