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, 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.

About the Technische Universität Dresden
The TU Dresden is among the top universities in Germany and Europe: strong in research, offering first-rate programmes of an overwhelming diversity, with close ties to culture, industry and society. As a modern full-status university with 14 departments, it offers a wide academic range making it one of a very few in Germany. TU Dresden is the largest university in Saxony. The big campus family of TU Dresden are 37.000 students, ca. 5.300 publicly funded staff members – among them 507 professors – and approximately 3.400 externally funded staff members.

On the 15th of June 2012 TU Dresden has succeeded in the Initiative for Excellence by the Federal Government in all funding lines with all its proposals. The institutional strategy "The Synergetic University", both proposals for clusters of excellence "Center for Advancing Electronics Dresden" (cfaed) and   “Center for Regenerative Therapies Dresden” (CRTD) as well as the Dresden International Graduate School for Biomedicine and Bioengineering (DIGS-BB) were approved. Now TUD is one of the eleven German universities that were identified as a “university of excellence”.

About the Leibniz Institute Dresden (IFW)
The Leibniz Institute for Solid State and Materials Research in Dresden – in short IFW Dresden – is a non-university research institute and a member of the G. W. Leibniz Scientific Community. It is concerned with modern materials science and combines explorative research in physics, chemistry and materials science with technological development of new materials and products. At present the IFW employs about 530 people, among them 200 scientists, mostly physicists, chemists and materials engineers. The annual budget of 29 Million Euro (2012) is supplied by the Federal government and by the German states in equal parts, the latter mainly by the Free State of Saxony. In addition to institutional funding, the IFW Dresden raises project resources of about 11 Million Euro per year.

Original publication:
Nature Materials, „Stacked topological insulator built from bismuth-based graphene sheet analogues“,
DOI: 10.1038/NMAT3570

Contact Persons:
Prof. Dr. Michael Ruck
Technische Universität Dresden

Tel. +49 351 463-33244

Prof. Dr. Jeroen van den Brink
IFW Dresden

Tel. +49 351 4659-400