Chance Effect of Lab's Fluorescent Lights Leads to Discovery

An accidental discovery of a "quantum Etch-a-Sketch" that may lead to the next generation of advanced computers and quantum microchips has been made by team of scientists from Penn State University and the University of Chicago. The researchers accidentally discovered a new way of using beams of light to draw and erase quantum-mechanical circuits on topological insulators, a unique class of materials with intriguing electronic properties.
The research, led by Nitin Samarth, professor and Downsbrough Head of Physics at Penn State, and David D. Awschalom, Liew Family Professor and deputy director in the Institute of Molecular Engineering at the University of Chicago, was published in the October 9 issue of Science Advances, an online journal of the American Association for the Advancement of Science.

The electrons in topological insulators have unique quantum properties that many scientists believe will be useful for developing spin-based electronics and quantum computers. However, making even the simplest experimental circuits with these materials has proved difficult because traditional semiconductor engineering techniques tend to destroy their fragile quantum properties. Even a brief exposure to air can reduce their quality.

The researchers discovered an optical effect that allows them to "tune" the energy of electrons in these materials using light, without ever having to touch the material itself. They have used this effect to draw and erase one of the central components of a transistor -- the p-n junction -- in a topological insulator for the first time.

Like many advances in science, the path to this discovery had an unexpected twist. "To be honest, we were trying to study something completely different," said Andrew Yeats, a graduate student in Awschalom's laboratory and the paper's lead author. "There was a slow drift in our measurements that we traced to a particular type of fluorescent lights in our lab. At first we were glad to be rid of it, and then it struck us -- our room lights were doing something that people work very hard to do in these materials." 

The researchers found that the surface of strontium titanate, the substrate material on which they had grown their samples, becomes electrically polarized when exposed to ultraviolet light, which their room lights happened to emit at just the right wavelength. The electric field from the polarized strontium titanate was leaking into the topological insulator layer, changing its electronic properties

The research was supported by the U.S. Office of Naval Research, Air Force Office of Scientific Research, and Army Research Office. Contact Nitin Samarth at