Nature Commun. 6, 6407 (2015)

Exciting physics often happens at interfaces. This can be taken quite literally in the case of surface plasmon polaritons — electromagnetic waves that can be excited at the interface between a metal and a dielectric, for example by irradiating with light. Direct observations of these quasiparticles are difficult to realize. But now, Luca Piazza and colleagues have found a way to both visualize the polaritons and control their spatial interference patterns.

The authors shot a femtosecond laser pulse at a silver nanowire suspended on a graphene film that was placed in a transmission electron microscope. The nanowire acted as a plasmonic nanoantenna, exciting surface plasmon polaritons that travelled back and forth and generated a standing light wave. Spatially resolving the electrons' energy losses (due to their interaction with the polaritons) led to images of the standing wave. Piazza et al. were able to show that by varying the polarization of the laser light, they could tune the nodal structure of the wave — capturing both the wave and particle nature of the polaritons.