A new theory by Rice University scientists could boost the growing field of spintronics, devices that depend on the state of an electron as much as the brute electrical force required to push it.
Materials theorist Boris Yakobson and graduate student Sunny Gupta at Rice's Brown School of Engineering describe the mechanism behind Rashba splitting, an effect seen in crystal compounds that can influence their electrons' "up" or "down" spin states, analogous to "on" or "off" in common transistors.
'Spin' is a misnomer, since quantum physics constrains electrons to only two states. But that's useful, because it gives them the potential to become essential bits in next-generation quantum computers, as well as more powerful everyday electronic devices that use far less energy.
However, finding the best materials to read and write these bits is a challenge.
The Rice model characterizes single layers to predict heteropairs—two-dimensional bilayers—that enable large Rashba splitting. These would make it possible to control the spin of enough electrons to make room-temperature spin transistors, a far more advanced version of common transistors that rely on electric current.
"The working principle behind information processing is based on the flow of electrons that can be either off or on," Gupta said. "But electrons also have a spin degree of freedom that can be used to process information and is the basis behind spintronics. The ability to control electron spin by optimizing the Rashba effect can bring new functionality to electronic devices.
"A cellphone with spin-related memory would be much more powerful and much less energy-consuming than it is now," he said.
Yakobson and Gupta would like to eliminate the trial and error of finding materials. Their theory, presented in the Journal of the American Chemical Society, aims to do just that.
"Electron spins are tiny magnetic moments that usually require a magnetic field to control," Gupta said. "However, manipulating such fields on the small scales typical in computing is very difficult. The Rashba effect is the phenomenon that allows us to control the electron spin with an easy-to-apply electric field instead of a magnetic field."
Yakobson's group specializes in atom-level computations that predict interactions between materials. In this case, their models helped them understand that calculating the Born effective charge of the individual material components provides a means to predict Rashba splitting in a bilayer.
