Article Source: Tokyo Institute of Technology, Center for Public Information
A new compound developed at Tokyo Tech shows highly unusual conducting properties that could be used in future electronic components. The details are described in the November 2013 issue of Tokyo Institute of Technology Bulletin:
Ordinary insulating solids, such as diamond, have energy bands that are fully occupied by electrons. The conducting band is so far away from the valence band in diamond that electrons do not have sufficient energy to move – the ‘band gap’ is large – therefore no electric current can be carried.
In recent years, researchers have become interested in materials called topological insulators (TIs), which act as insulators on the inside, but are highly conductive on their surfaces. In TIs, an exceptionally strong spin-orbit interaction inverts the energy gap between occupied and empty states, so that electrons at the surface can flow across the gap. These properties are intrinsic to the material, meaning a TI remains conductive even if its surface is not perfect.
Now, an international team of scientists from Japan, the UK and the USA, led by Takao Sasagawa at Tokyo Institute of Technology, have successfully developed a new TI from bismuth, tellurium and chlorine (BiTeCl). Their new TI is inversion asymmetric, meaning it has different electronic states, and therefore different polarities, on each crystal surface. As a result, it exhibits many topological effects that have not been seen experimentally before.