Generating, sustaining electrical currents with unique properties for information processing closer to reality

January 30, 2013, Agency for Science, Technology and Research (A*STAR), Singapore
Semiconductor physics: Taking control of spin
Sustaining a spin-polarized current, in which the spin (depicted as an arrow) of each electron (yellow) is aligned, is integral to advancing spintronic applications. Credit: 2013 A*STAR Data Storage Institute

Spintronics is a form of signal processing similar to that used in traditional electronics, but it takes advantage of a property of electrons known as spin. Spin is often visualized as an arrow about which the electron rotates, much like a top spinning around its axis. Generating a stream of electrons in which these 'arrows' are all parallel—a so-called spin-polarized current (see image)—is the foundation upon which spintronics is based. Imperfections in a material, however, can easily destroy polarization. Simply applying an oscillating voltage across the device could help to maintain a spin-polarized current even in the presence of impurities, according to theoretical research by Seng Ghee Tan at the A*STAR Data Storage Institute, Singapore, and co‐workers.

Tan and his colleagues considered a two-dimensional electron gas: a system in which the electrons can move only in one plane. When a spin-polarized current flows through such a material, the spins interact with the electron's motion through an effect known as Rashba spin–orbit coupling. This makes the spins start to 'wobble' or precess: at first they point upwards but then point downwards, and this reduces the total spin polarization to zero. "We want to prolong the of a spin current in the channel by controlling the strength of the Rashba coupling," says Tan. To this end, he and his team investigated a device, known as a spin-current rectifier, that lets a spin current flow with one particular polarization—upwards only, for example.

The researchers developed a simple that predicts the behavior of the spin current as an alternating voltage is applied across the device. Their model shows that when the frequency of the voltage is zero, the spin polarization goes back and forth as expected. "However, by increasing the frequency, we see an increasingly asymmetrical pattern of in favor of positive ," explains Tan. "We call this a gradual process of rectification."

Their approach can even suppress precessional motion entirely. When the external modulation frequency is much faster than the natural precessional frequency of the spins, known as the Larmor frequency, the spins have no time to change direction so remain pointing upwards. Consequently, the system maintains a spin-polarized current.

Once spin currents can be sustained, spintronics will have all the potential of electronics with the additional advantage of an extra degree of control. The spin-current rectifier investigated by Tan and his co-workers could therefore become a vital component in this future technology.

Explore further: Spin polarized supercurrents optimized with a simple flip

More information: Ho, C. S., Jalil, M. B. A. & Tan, S. G.  Sustainable spin current in the time-dependent Rashba system. Journal of Applied Physics 111, 07C327 (2012).

Related Stories

Spin polarized supercurrents optimized with a simple flip

May 14, 2012

( -- Researchers from Michigan State University, the NIST Center for Neutron Research, and the NIST Center for Nanoscale Science and Technology have discovered the key to controlling and enhancing the lossless flow ...

Spin-polarized electrons on demand

January 21, 2009

Many hopes are pinned on spintronics. In the future it could replace electronics, which in the race to produce increasingly rapid computer components, must at sometime reach its limits. Different from electronics, where whole ...

Spin-polarized electrons on demand

January 15, 2009

Many hopes are pinned on spintronics. In the future it could replace electronics, which in the race to produce increasingly rapid computer components, must at sometime reach its limits. Different from electronics, where whole ...

Spin polarization achieved in room temperature silicon

November 27, 2009

( -- A group in The Netherlands has achieved a first: injection of spin-polarized electrons in silicon at room temperature. This has previously been observed only at extremely low temperatures, and the achievement ...

Recommended for you

Information engine operates with nearly perfect efficiency

January 19, 2018

Physicists have experimentally demonstrated an information engine—a device that converts information into work—with an efficiency that exceeds the conventional second law of thermodynamics. Instead, the engine's efficiency ...

Team takes a deep look at memristors

January 19, 2018

In the race to build a computer that mimics the massive computational power of the human brain, researchers are increasingly turning to memristors, which can vary their electrical resistance based on the memory of past activity. ...

Artificial agent designs quantum experiments

January 19, 2018

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.