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Posted: Mar 18, 2013

Honeycomb Nets from Bismuth Cubes: A New Prospect for Nanoelectronics

(Nanowerk News) Researchers from Dresden discover a new material that conducts electric currents without loss of power over its edges and remains an insulator in its interior. The material is made out of bismuth cubes packed in a honeycomb motif that is known from the graphene structure. As opposed to graphene, the new material exhibits its peculiar electrical property also at room temperature and, hence, holds big promises for applications in nanoelectronics.
Researchers from the TU Dresden and the Leibniz Institute for Solid State and Materials Research, both in Dresden, have synthesized a new material that on the atomic level resembles graphene, a honeycomb net from carbon atoms. The new material is built mainly by atoms of the heavy element bismuth. Whereas a honeycomb-like sheet is formed by carbon atoms in graphene, the honeycomb net in the new material is assembled from bismuth cubes The researchers in Dresden are particularly excited about their discovery because the electrons inside their bismuth-based material form a new and exotic quantum state of matter. The joint paper by the groups of Prof. Michael Ruck from the Institute of Inorganic Chemistry, TU Dresden, and Prof. Jeroen van den Brink, IFW Dresden, recently published in Nature Materials ("Stacked topological insulator built from bismuth-based graphene sheet analogues"), reports that the new material is made out of sheets of a so-called topological insulator, which has the property that electric currents can flow on its edges without loss of power.
What is a topological insulator? Traditionally materials are classified according to their conducting properties as either electrical conductors or insulators. Within this classification semiconductors are considered to be a special type of insulator. Topological insulators are described by physicists as a third state of matter the interior of which is perfectly insulating, while its outside surface and/or edges are conducting. Noteworthy is that the electric currents on the conducting surface and/or edges of a topological insulator can run unimpeded. This characteristic gives topologically insulating materials great potential for use in future microelectronic transistors and sensors that are highly energy efficient.
„Graphene was the first material predicted to be a topological insulator, but such an exotic state could only exist at extremely low temperatures, very close to the absolute zero of temperature“, explains Professor Ruck the motivation behind the search for a suitable material. „The structure and topological properties of the discovered new material from bismuth cubes are related to those of graphene. However, our material has the remarkable advantage of being a topological insulator at room temperature.“
Each electron carries besides an electrical charge also a magnetic moment, the spin of the electron. In a normal metal, such as copper, the electron spins point in an arbitrary direction. But electrons traveling in the same direction along the metallic edges of the bismuth cubes in the new material are very different in this respect: They spontaneously align their spins. This effect is due to the exotic quantum nature of the topological insulator. What is more, when these electrons change their direction of motion along the edge, their spins are also collectively reversed. Hence electrons that travel along the edge in opposite directions also have opposite spin orientations.
The spin-alignment of electrons that carry an electric current is an appealing feature for spintronics, an emerging information-processing technology that relies on the control of the intrinsic spin of electrons to build efficient computing and memory devices.
Both Michael Ruck and Jeroen van den Brink stand proud of the results of their close cooperation. „The excellent research environment and the strong scientific partnership in Dresden were essential for success“, emphasizes Professor Jeroen van den Brink, a director of the Institute for Theoretical Solid State Physics at the Leibniz Institute Dresden.
Source: Technische Universität Dresden
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