Extraordinary physics behavior in a “topological surface state” observed
Topological surface states
Topological surface states are a class of novel electronic states. Unlike conventional two-dimensional electron states, these surface states are expected to be immune to localization and to overcome barriers caused by material imperfection.
In the conventional two-dimensional electron states, electron flow in materials is impeded by imperfections — seemingly slight edges and rifts act like cliffs and crevasses in this microscopic world, blocking electrons in their path. However recent theories, predict that in some compounds containing elements such as antimony there exist topological surface states where in electrons on the surface of these materials are not impeded by the material imperfections. These electron states in fact transmit through naturally occurring surface defects and are immune to disruptions in their flow.
Extraordinary physics behavior in a “topological surface state” observed
Now for the first time a team of Princeton University scientists have observed the extraordinary physics behavior in a “topological surface state” on a microscopic wedge of the metal antimony. The researchers used a scanning tunnelling microscope to measure the transmission and reflection probabilities of topological surface states of antimony through naturally occurring crystalline steps separating atomic terraces. The scientists observed that the topological surface states of antimony penetrate barriers such as the crystalline steps with high probability.
With lab instruments, the team was able to measure how long electrons are staying in a region of the material and how many of them flow through to other areas. The results showed a surprising efficiency by which surface electrons on antimony go through barriers that typically stop other surface electrons on the surface of most conducting materials, such as copper.
Commenting on their observation of the “topological surface state” in antimony lead researcher, physics Professor Ali Yazdani said, “Material imperfections just cannot trap these surface electrons. This demonstration suggests that surface conduction in these compounds may be useful for high-current transmission even in the presence of atomic scale irregularities — an electronic feature sought to efficiently interconnect nanoscale devices.”
About the experiment, Robert Cava, Professor of Chemistry at Princeton said, “shows for the first time that the theoretically predicted immunity of topological surface states to death at the hands of the ever-present defects in the atomic arrangements on crystal surfaces is really true.”
The antimony crystals for the work were grown in the laboratory of Cava. Yazdani’s team worked in the specially designed Princeton Nanoscale Microscopy Laboratory, where highly accurate measurements at the atomic scale are possible because sounds and vibrations, through a multitude of technologies, are kept to a minimum. They used a powerful scanning tunneling microscope to view electrons on the surface of the antimony sample.
Researchers on the team include: Yazdani; postdoctoral fellows Jungpil Seo and Haim Beidenkopf; graduate student Pedram Roushan; and, along with Cava, his former postdoctoral fellow Yew San Hor, who is now at the Missouri University of Science and Technology.
Source: http://www.princeton.edu/main/news/archive/S27/90/58A67/
July 15, 2010