Physicists Present Latest Results in Graphene and Metamaterials Research
Cutting‑edge research on new materials is a major focus of the annual APS March Meeting, and the 2007 conference in Denver was no exception. Among the more interesting highlights was a series of papers reporting new results in the areas of metamaterials–also known as “left‑handed materials”–and graphene.
Metamaterials are amalgams of tiny rods, strips and rings that exhibit a negative index of refraction, thanks to their unusual, nanoscale‑engineered architecture, which enhances the magnetic interaction between light and matter. To bring about a negative‑index condition, the material’s electric permittivity must be negative, and in some cases, also its magnetic permeability.
Metamaterials made their debut at the APS March meeting in 2000. At the time, only a couple of research groups were working in this area; today there are dozens investigating ways to exploit the unique properties of these materials to produce perfect lensing and other odd optical properties.
At the APS meeting in Denver, Purdue University’s Vladimir Shalaev reported on a new record‑setting metamaterial that might be ideal for so‑called “superlensing”: a process in which a thin flat panel of the metamaterial would be able to image an object at a spatial resolution better than the wavelength of the illuminating light. Ever since metamaterials were first realized in the laboratory, physicists have been pushing the boundary of these “left‑handed” materials to shorter and shorter wavelengths.
Shalaev and his colleagues have reported a negative‑index material operating at a wavelength of 770 nm, the shortest yet observed for a single‑negative material (exhibiting only negative permittivity). Using the same material with a different light polarization, they achieved a wavelength of 815 nm, the shortest yet observed for a double‑negative material (exhibiting both negative permittivity and permeability).
An even hotter research topic these days is graphene, essentially one‑atom‑thin carbon sheets. Physicists are also excited about the very unusual behavior of electrons moving through a graphene landscape: namely, you can increase the electrons’ energy without increasing their velocity, almost as if the electrons were behaving like slow‑moving light waves.
At last year’s March Meeting in Baltimore, there were presentations on graphene by only a few groups. This year, there were dozens. Graphene‑related research has exploded, thanks in part to its adaptable mechanical and electrical properties, with some 180 research papers published on the topic in the past year, mostly on the theoretical aspects, but progress has also been made on the experimental front.
In Denver, Pablo Jarillo‑Herrero of Columbia University gave an overview of the latest experimental developments in this rapidly growing field. For instance, researchers have successfully developed graphene ribbons. Among the more interesting recent findings is that the resistivity of the material changes according to the width of the ribbons, which means that the semiconducting properties of graphene could be tailored to suit the application.
Jarillo‑Herrero also summarized other recent progress in the field, including the observation of superconducting graphene transistors by researchers at Delft University in the Netherlands; freely suspended graphene sheets, a room‑temperature Hall effect, and room‑temperature single‑electron transistors with graphene–the latter by a research group at the University of Manchester in England.
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Contributing Editor: Jennifer Ouellette
Staff Writer: Ernie Tretkoff