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Novel transistor exhibits quantum spin Hall effect

Posted: 24 Feb 2015 ?? ?Print Version ?Bookmark and Share

Keywords:MIT? quantum spin Hall effect? transistor? TFET? transition metal dichalcogenide?

A team of MIT researchers has discovered an innovative transistor that harnesses a new effect, called the quantum spin Hall effect, to create a topological field effect transistor (TFET). Xiaofeng Qian has since moved to the recently established department of materials science and engineering at Texas A&M University where the Texas Advanced Computer Centre (TACC) validated the researcher's results.

Xiaofeng Qian

Xiaofeng Qian

"We found that when deposited in a flat sheet just three atoms thick, our crystalline lattices exhibited a new electronic effect we call the quantum spin Hall effect," said professor Xiaofeng Qian.

In bulk topological materials such as the transition metal dichalcogenide (TMDC) used here, they conduct on the top and bottom, but are insulators in their interiors. What Qian and colleagues discovered was that when thinned down to just three-atomic-layers thick, they conducted only on the edges and not in the middle. What's more their conduction could be switched, turned on and off with a gate, like a normal FET just by applying a perpendicular electrical field. Even more unusual, making the TFET a spintronic device, was that the electrons conducting along the edges travelled in different directions depending upon their spin.

Topological phases in the 2D TMDC

Topological phases in the 2D transition metal dichalcogenide (TMDC) can be turned on and off by simply applying a vertical electric field shown here by the red crossing lines that conduct electricity along the edges of the material when the electric field is turned off. When the electric field is turned on the red lines are broken and a black gap appears between the valence and conducting bands of TMDC, which indicate the edges no longer conduct. (Credit: Qian et. al.) (Source: Texas A&M University)

"What's more the electrons with up spin flow in one direction, while those with down spin flow in the opposite direction. So by controlling the injection of charged carriers, we can create a spintronic transistor," noted Qian.

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