The work is based on topological insulators, which are insulators on the inside, but conduct on their surface. One property of topological insulators is that an electron must travel in a specific direction along their surface, determined by its spin direction – or ‘spin-momentum locking’.
“The surface of a topological insulator is like a well-organised 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,” said researcher Yuqing Huang. However, one issue is how to generate and manipulate the surface spin current.
The research team says it has taken the first step towards transferring spin-oriented electrons between a topological insulator and a conventional semiconductor by generating electrons with the same spin in gallium arsenide. To achieve this, they used circularly polarised light, in which the electric field rotates either clockwise or anticlockwise when seen in the direction of travel of the light. Spin-polarised electrons could then be transferred from GaAs to a topological insulator, to generate a directional electric current on the surface.
According to the team, it could control the orientation of spin of the electrons and the direction and the strength of the electric current in the topological insulator bismuth telluride without applying an external electric voltage. This is said to be significant for the design of opto-spintronic devices that exploit the interaction of matter with light.
"We have combined the superior optical properties of GaAs with the electrical properties of a topological insulator,” said Professor Wemin Chen. “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.”
