MIT researchers have identified a new material that shares many of graphene’s interesting properties. Writing in Nano Letters, the researchers describe how thin films of bismuth-antimony share a property with graphene called two-dimensional Dirac cones.
A 2D Dirac cone, being two dimensional, is not a literal cone. It is named for the shape of the graph you get if you plot the energy against momentum of an electron moving through a material, and illustrates the electronic band structure of the material.
The researchers, materials science and engineering PhD candidate Shuang Tang and Institute Professor Mildred Dresselhaus, explain in the announcement that this property allows an electron to travel through the material "like a beam of light", so that the electron flow in a potential future device could be many hundreds of times that of anything based on conventional silicon technology.
From the release: Similarly, in a thermoelectric application — where a temperature difference between two sides of a device creates a flow of electrical current — the much faster movement of electrons, coupled with strong thermal insulating properties, could enable much more efficient power production. This might prove useful in powering satellites by exploiting the temperature difference between their sunlit and shady sides, Tang says.
The properties of the bismuth-antimony films can also be controlled post production, by varying the ambient conditions. The thickness of the film as well as the orientation of its growth will also have an impact on its properties, the researchers said. This means that electrons flowing in one direction in the material may obey the classical laws of physics, while those moving perpendicularly might obey relativistic laws.
Professor Dresselhaus is clear that no such devices have yet been built, but she wants everyone to watch this space, adding that the necessary analysis could probably be done within a year.
Fellow academic Joseph Heremans, a physics proffessor at Ohio State University, notes that many of bismuth’s unusual properties have been known for some time, but "what is surprising is the richness of the system calculated by Tang and Dresselhaus. The beauty of this prediction is further enhanced by the fact that system is experimentally quite accessible…This paper should stimulate a large experimental effort."