Distance-dependent photo-induced electron transport in nanometer-sized junctions

We describe photo-induced current experiments observed in nm-sized electro-migrated nano gaps, using surface plasmon polaritons (SPPs) as the source of the optical driving field. For gaps smaller than 5 nm, we observe a stable photo-induced current that is linear with the intensity of the SPP mode, whereas the photo-current in wider gaps shows a highly nonlinear dependence that is reminiscent of field emission. The results are explained by a modified Wentzel–Kramers– Brillouin tunneling model, which reproduces the observed transition from optical rectification to optically driven field emission in the nano junction.