Sep. 18, 2012 at 3:11 PM ET
Scientists have harnessed an imaging technique to create a 3-D visualization of electrons moving at nearly light speed on and in a futuristic material that could replace silicon in electronic devices of tomorrow.
The technique can capture increments of time at the level of femtoseconds — that is millionths of a billionth of a second. By stitching together these images, they are able to create movies of electrons as they scatter in response to a short pulse of light.
The interior of the futuristic material, called topological insulators (TIs), almost completely blocks any flow of electrons, but the surface is a conductor that allows electrons to travel at almost the speed of light unimpeded by impurities.
“Because of these characteristics, TIs are seen as a promising new material for electronic circuits and data storage devices,” the Massachusetts Institute of Technology explains in a press release.
“But developing such new devices requires a better understanding of exactly how electrons move around on and inside the TI, and how the surface electrons interact with those inside the material.”
A research team, led by graduate student Yihua Wang and assistant professor of physics Nuh Gedik at MIT, have done just that using the “pump-probe” technique they pioneered to create 3-D images of the energy, momentum and spin of electrons within topological insulators.
The university describes the technique this way:
It uses a short pulse of laser light to energize the material, causing electrons to scatter, and a second, slightly delayed pulse to illuminate it and produce an image. “The first pulse does something to the electrons, and the second pulse captures what happened,” Gedik explains.
Then, the process is repeated, with the second laser pulse delayed by ever-increasing increments of just a few femtoseconds. Each resulting image shows the response of the electrons to the beam after a corresponding interval. These images can then be assembled into a movie that shows how the response changes with time.
Using the technique, the researchers found that electrons on the topological insulator surface interact with interior electrons via sound waves and the interaction happens more intensely at high temperatures.
Understanding these interactions, Gedik notes, will help shape future work on topological insulators. Current proposals for futuristic data storage devices made with the material, for example, are based on the behavior of surface electrons.