拓扑绝缘体的不对称性

New research shows that a class of materials being eyed for the next generation of computers behaves asymmetrically at the sub-atomic level. This research is a key step toward understanding the topological（拓扑的，地质学的） insulators that may have the potential to be the building blocks of a super-fast quantum computer that could run on almost no electricity. Scientists from the Energy Department's National Renewable Energy Laboratory contributed first-principles calculations and co-authored the paper "Mapping the Orbital Wavefunction of the Surface States in 3-D Topological Insulators," which appears in the current issue of Nature Physics. A topological insulator is a material that behaves as an insulator in its interior but whose surface contains conducting states.

In the paper, researchers explain how the materials act differently above and below the Dirac point and how the orbital and spin texture of topological insulator states switched exactly at the Dirac point. The Dirac point refers to the place where two conical forms -- one representing energy, the other momentum -- come together at a point. In the case of topological insulators, the orbital and spin textures of the sub-atomic particles switch precisely at the Dirac point. The phenomenon occurs because of the relationship between electrons and their holes in a semiconductor.

This research is a key step toward understanding the topological insulators like bismuth selenide (Bi2Se3), bismuth telluride (Bi2Te3), antimony telluride (Sb2Te3), and mercury telluride (HgTe) that may have the potential to be the building blocks of a quantum computer, a machine with the potential of loading the information from a data center into the space of a laptop and processing data much faster than today's best supercomputers.

"The energy efficiency should be much better," said NREL Scientist Jun-Wei Luo, one of the co-authors. Instead of being confined to the on-and-off switches of the binary code, a quantum computer will act more like the human brain, seeing something but imagining much more, he said. "This is entirely different technology."

Topological Insulators are of great interest currently for their potential to use their exotic properties to transmit information on electron spins with virtually no expenditure of electricity, said Luo. NREL's Xiuwen Zhang is another co-author as are scientists from University of Colorado, Rutgers University, Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, and the Colorado School of Mines. Luo and Zhang work in NREL's Center for Inverse Design, one of 46 Energy Frontier Research Centers established around the nation by the Energy Department's Office of Science in 2009 to accelerate basic research on energy.