Watching electrons move at high speed

Topological insulators are exotic materials, discovered just a few years ago, that hold great promise for new kinds of electronic devices.

The unusual behaviour of electrons within them has been very difficult to study, but new techniques developed by a team of researchers at MIT could help unlock the mysteries of exactly how electrons move and react in these materials, opening up new possibilities for harnessing them.

For the first time, the MIT team has managed to create three-dimensional ''movies'' of electron behaviour in a topological insulator, or TI.

The movies can capture vanishingly small increments of time - down to the level of a few femtoseconds, or millionths of a billionth of a second - so that they can catch the motions of electrons as they scatter in response to a very short pulse of light.

Electrons normally have mass, just like many other fundamental particles, but when moving along the surface of TIs they move as if they were massless, like light - one of the extraordinary characteristics that give these new materials such promise for new technologies.

The dramatic new results are published this week in the journal Physical Review Letters, in a paper by MIT graduate student Yihua Wang, assistant professor of physics Nuh Gedik and six other researchers.