Scientists move towards spintronics based devices

Scientists have gained further ground in the development of topological insulators that are able to act as both insulators and conductors, offering possibilities for low power electronics devices based on spintronics.

The materials are able to simultaneously prevent the flow of electrical current in their interior, while allowing the transportation of spin-polarised electrons which prevents the unwanted scattering of electrons that occurs with power consumption.

This means that topological insulators could potentially offer use in transistors and memory devices in the future that are extremely energy efficient.

The team at UCLA’s Henry Samueli School of Engineering and Applied Science and the Australia’s University of Queensland have now shown the potential of surface conduction channels in topological insulator nanoribbons made of bismuth telluride, and demonstrated how the surface states are able to be turned on and off depending on the position of the Fermi level.

“Our finding enables a variety of opportunities in building potential new-generation, low-dissipation nanoelectronic and spintronic devices, from magnetic sensing to storage,” said Kang L. Wang, Professor of Electrical Engineering at UCLA Engineering.

Bismuth telluride is a thermoelectric material which has been predicted to be a three dimensional topological insulator, though the scientists state that there have been problems with modifying the surface conduction of the material.

The development of topological nanoribbons has apparently helped with this, as their large surface-to-volume ratios are able to enhance surface conditions and enable manipulation by external means.

The team used thin bismuth telluride nanoribbons as conducting channel in field-effect transistor structures, which according to the researchers rely on an electric field to control the Fermi level and so the conductivity of the channel.

This meant that the researchers were able to, for the first time, demonstrate the ability to control surface states in topological insulator nanostructures.

“We have demonstrated a clear surface conduction by partially removing the bulk conduction using an external electric field,” said Faxian Xiu, a UCLA staff research associate and lead author of the study.

“By properly tuning the gate voltage, very high surface conduction was achieved, up to 51 percent, which represents the highest values in topological insulators.”

“This research is very exciting because of the possibility to build nanodevices with a novel operating principle,” said Wang, adding that that, like graphene, topological insulators could be made in high speed transistors and ultra-high sensitivity sensors.

It is said that the next step for Wang’s team is to produce high-speed devices based on their discovery.

“The ideal scenario is to achieve 100 percent surface conduction with a complete insulating state in the bulk,” Xiu said.

“Based on the current work, we are targeting high-performance transistors with power consumption that is much less than the conventional complementary metal-oxide semiconductors (CMOS) technology used typically in today’s electronics.”