Bringing photons to the point
This problem has now been solved with the aid of a tiny metal pin with a nanometer-sized tip. Acting like a lightning rod, it concentrates incident light into a very small volume. This raises the momentum of infrared photons by up to 60-fold, giving them the extra momentum they need to launch plasmonic waves along the graphene layer. For this purpose, the researchers made use of a commercial infrared scanning near-field microscope, whose finely honed scanning tip is normally used to map the chemical composition of a material under test
In this case only the edge zone of a graphene sample was imaged. Reflection of the plasmons at this edge produces an interference pattern, which encodes information that can be used to confirm formation of the plasmons. It also allows one to deduce many of their properties, such as the magnitude of the reflection at the graphene edge and the change in the velocity by external electric bias, which is of particular interest for future applications. "The long-sought ability to control light signals by electrical means has thus been realized," says Keilmann.
An independent study carried out by a Spanish group, based on the use of a graphene sheet formed by deposition from the gas phase rather than the exfoliated film used in the LMU work, comes to a similar conclusion. The two papers have now appeared back-to-back in the top-tier journal Nature, underlining the significance of these findings for the field of nanoelectronics.
|Contact: Luise Dirscherl|