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Utah Engineers Pioneer New Field in Materials Science

Photonics.com
Feb 2013
SALT LAKE CITY, Feb. 20, 2013 — Shuttling information at the speed of light in quantum computers and other high-speed electronic devices may be feasible with organic materials that conduct electricity on their edges, but acts as an insulator inside, new theoretical calculations predict.

The University of Utah study of these materials, called organic topological insulators, will help pioneer a new field of research in materials science, much as organic materials lowered the cost and eased production of LEDs and solar cells, said Feng Liu, professor and chair of materials science and engineering.

“This is the first demonstration of the existence of topological insulators based on organic materials,” Liu said. “Our findings will broaden the scope and impact of these materials in various applications from spintronics to quantum computing.”


University of Utah engineers demonstrated that it is feasible to build the first organic materials that conduct electricity on their molecular edges, but act as an insulator inside. Called organic topological insulators, these materials are made from a thin molecular sheet (left) that resembles chicken wire and conducts electricity on its right edge (blue line) — with the electrons carrying more information in the form of "up" spin. These new materials could be used to shuttle information at the speed of light in quantum computers due to the unique physical behavior of a special class of electrons called Dirac fermions, depicted (right) in a plot of their energy and momentum. Courtesy of Zhengfei Wang and Feng Liu, University of Utah 

Many researchers must synthesize the new organic topological insulators, but Liu said his team’s previous work “shows we can engineer an interface between two different thin films to create topological insulators" in which electrons known as Dirac fermions move along the interface between two films.

Theoretical calculations performed by Liu and colleagues at the university’s College of Engineering predicted the existence of an organic topological insulator using molecules with carbon-carbon bonds and carbon-metal bonds, called an organometallic compound. For this new study, how Dirac fermions move along the edges of this compound — which looks like a sheet of chicken wire — were investigated.

To generate a topological insulator, materials that can transmit fermions must be designed. In a topological insulator, fermions behave like a massless or weightless packet of light, conducting electricity as they move very fast along a material's surface or edges. When these fermions venture inside the material, however, this "weightless" conductivity screeches to a halt.

What's more, Dirac fermions have a property called spin, or angular momentum around the particle's axis that behaves like a magnetic pole. This property gives investigators another way to place information into a particle because the spin can be switched "up" or "down." Such a mechanism could be useful for spin-based electronic devices, or spintronics, which can store information both in the charge and the spin of electrons.

“We have demonstrated a system with a special type of electron — a Dirac fermion — in which the spin motion can be manipulated to transmit information,” Liu said. “This is advantageous over traditional electronics because it's faster and you don't have to worry about heat dissipation.”

Earlier this year, the researchers discovered a "reversible" topological insulator in a system of bismuth-based compounds in which the behavior of ordinary or Dirac fermions could be controlled at the interface between two thin films. Bismuth is a metal best known as an ingredient of Pepto-Bismol. These theoretical predictions were confirmed experimentally by co-authors from Shanghai Jiaotong University in China.

Although inorganic topological insulators based on different materials have been studied for the past decade, organic or molecular topological insulators have not.

Results of the study were published in Nature Communications (doi:10.1038/ncomms2451).  

For more information, visit: www.coe.utah.edu


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