Computers today are based on electric charge, the property of an electron that makes it move if an electric field is applied. However, physicists have known since the 1920s that electrons not only have a charge but also a quantum mechanical property called a spin. The spin causes electrons to act like tiny magnets. While computers today depend on the charge of electrons, scientists have started to explore how the electron spin might be used to build faster, more robust versions of modern electronics or to develop technologies with completely new capabilities. Recently, researchers from Princeton University found that they could use an exotic material called a topological insulator, discovered less than a decade ago, to build a device that generates electron currents with different spin on demand. “Topological insulators are amazing materials where the direction of motion of the electron is locked to its spin, so that the spin remains stable as long as you keep the electron moving in the same direction. Because of this property, topological insulators were a natural starting point for us to develop a device where we could tune the electron spin for use in computers,” said senior researcher Dr. Madhab Neupane of Princeton University, who carried out the study. The team of researchers included scientists from universities in the United States, Taiwan, Singapore, Germany and Sweden and used a technique called photoelectron spectroscopy available at Beamline I3 at MAX-lab to study the properties of electrons in the topological insulator device.
A new spin on the electron
The key insight in building the device was to use a very thin sheet of a topological insulator. While a bulk topological insulator is effective at locking the momentum to the spin, this property disappears for a topological insulator which is too thin.
However, it turns out that some electrons lose the spin locking property faster than others. “We found that there are some electrons which lose the spin locking property very quickly, so that as soon as you take a thin sheet of topological insulator, those electrons basically behave like normal electrons in an ordinary wire. On the other hand, other electrons have a more robust spin locking property, which disappears more gradually,” said Dr. Neupane. The results of the study suggest that applying a voltage to the thin sheet of topological insulator can select between electrons with different spins. If the voltage changes over time, the electron spin signal will also change over time in exactly the same way. This could allow researchers to encode an electric voltage signal as an electron spin signal.“Through future research, we could use this device to convert the signals used in electronics today into spin signals used by technologies of the future,” said Dr. Neupane. As scientists and engineers develop technologies, which go beyond conventional electronics, this work could provide a new tool to use for manipulating electron spin.