'Conducting on the outside, insulating on the inside' is probably the most simplistic way to describe topological insulators. These odd materials discovered just years ago have different electrical properties depending on if you are on their surface or within their volume, but their mystery does not end there. The conducting surface of the material also has the special property of conducting electrons as though they were massless, a property graphene also has. Altogether, these properties make the materials very interesting to those trying to develop future electronics, and researchers at MIT have recently completed a study to help the development process.
With such drastically different electron behaviors present in topological insulators, it is important to know how electrons in the two realms interact. To do this the researchers used a pump-probe experiment with the ability to make instantaneous observations of the electrons' energy, momentum, and spin. An initial laser pulse excites the electrons while a second laser pulse actually collects the information. After repeating the process with different delays between the pulses, the researchers were able to create a video of the electrons scattering and returning to their former positions.
The observations show the surface electrons actually scatter into the volume when they are excited, which is important to know when designing a component based on topological insulators. The researchers also discovered that the amount of scattering depends on the temperature of the material, with colder temperatures allowing less scattering.