Discovering how to control and transfer spinning electrons opens the door for unique hybrid devices that could outpace current semiconductor electronics. In a research paper published in Nature Communications, Researchers at Linköping University in Sweden reveal how to integrate a regularly used semiconductor with a topological insulator, a newly discovered state of matter with exclusive electrical properties.
The Researchers have taken the first step towards transferring spin-oriented electrons between a topological insulator (orange layer) and a conventional semiconductor (blue layer). (Credit: Linkoping University)
An electron spins around its own axis just like the Earth, in a clockwise or counter-clockwise direction. “Spintronics” is the name used to define technologies that utilize both the electron’s spin and charge. Existing applications are inadequate and the technology is largely used in computer hard drives. In contrast to conventional electronics, spintronics potentially has great advantages including higher speed and lower power consumption.
In relation to electrical conduction, natural materials are divided into three categories: insulators, conductors and semiconductors. Researchers have lately discovered an unusual phase of matter known as “topological insulators”, which is an insulator on the inside, but a conductor on the outside. One of the most prominent properties of topological insulators is that an electron has to travel in a specific direction along the surface of the material, defined by its spin direction. This property is referred to as “spin-momentum locking”.
The surface of a topological insulator is like a well-organized divided highway for electrons, where electrons having one spin direction travel in one direction, while electrons with the opposite spin direction travel in the opposite direction. They can travel fast in their designated directions without colliding and without losing energy.
Yuqing Huang, PhD Student, Department of Physics, Chemistry and Biology (IFM) at Linköping University
With these properties, topological insulators hold great potential for use in spintronic applications. However, one main question is how to generate and regulate the surface spin current in topological insulators.
The research team behind the present study has currently taken the first step towards moving spin-oriented electrons between a topological insulator and a conventional semiconductor. They produced electrons with the same spin in gallium arsenide, GaAs, a semiconductor usually used in electronics. To accomplish this, they used circularly polarized light, in which the electric field rotates either counter-clockwise or clockwise when seen in the direction of travel of the light. The spin-polarized electrons could then be moved from GaAs to a topological insulator, to make a directional electric current on the surface. The team could control the orientation of spin of the electrons, and the strength and direction of the electric current in the topological insulator bismuth telluride, Bi
2Te 3. According to the Researchers, this flexibility has not been available before. All of this was attained without applying an external electric voltage, showing the potential of efficient change from light energy to electricity. The findings are noteworthy for the design of original spintronic devices that make the most of the interaction of matter with light, a technology known as “opto-spintronics”.
We combine the superior optical properties of GaAs with the unique electrical properties of a topological insulator. This has given us new ideas for designing opto-spintronic devices that can be used for efficient and robust information storage, exchange, processing and read-out in future information technology.
Professor Weimin Chen, Leader of the study
The research was performed in partnership with Researchers from the Chinese Academy of Sciences in Shanghai. It was financed with support from, among others, the Swedish Research Council, the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University, the Swedish Foundation for Strategic Research and the Natural Science Foundation of China.