IBM creates consistent electron spin inside semiconductors, takes spintronics one twirl closer
A fundamental challenge of developing spintronics, or computing where the rotation of electrons carries instructions and other data rather than the charge, has been getting the electrons to spin for long enough to shuttle data to its destination in the first place. IBM and ETH Zurich claim to be the first achieving that feat by getting the electrons to dance to the same tune. Basing a semiconductor material on gallium arsenide and bringing the temperature to an extremely low -387F, the research duo have created a persistent spin helix that keeps the spin going for the 1.1 nanoseconds it would take a normal 1GHz processor to run through its full cycle, or 30 times longer than before. As impressive as it can be to stretch atomic physics that far, just remember that the theory is some distance from practice: unless you're really keen on running a computer at temperatures just a few hops away from absolute zero, there's work to be done on producing transistors (let alone processors) that safely run in the climate of the family den. Assuming that's within the realm of possibility, though, we could eventually see computers that wring much more performance per watt out of one of the most basic elements of nature.
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IBM Scientists "Waltz" Closer to Using Spintronics in Computing
- IBM Research is the first to synchronize electron spins and image the formation of a persistent spin helix.
- Spintronics could enable a new class of magnetic-based semiconductor transistors resulting in more energy efficient electronic devices.
Until now, it was unclear whether or not electron spins possessed the capability to preserve the encoded information long enough before rotating. Unveiled in the peer-reviewed journal Nature Physics, scientists from IBM Research and the Solid State Physics Laboratory at ETH Zurich demonstrated that synchronizing electrons extends the spin lifetime of the electron by 30 times to 1.1 nanoseconds -- the same time it takes for an existing 1 GHz processor to cycle.
Today's computing technology encodes and processes data by the electrical charge of electrons. However, this technique is limited as the semiconductor dimensions continue to shrink to the point where the flow of electrons can no longer be controlled. Spintronics could surmount this approaching impasse by harnessing the spin of electrons instead of their charge.
This new understanding in spintronics not only gives scientists unprecedented control over the magnetic movements inside devices but also opens new possibilities for creating more energy efficient electronics.
The Spintronics Waltz
A previously unknown aspect of physics, the scientists observed how electron spins move tens of micrometers in a semiconductor with their orientations synchronously rotating along the path similar to a couple dancing the waltz, the famous Viennese ballroom dance where couples rotate.
Dr. Gian Salis of the Physics of Nanoscale Systems research group at IBM Research – Zurich explains, "If all couples start with the women facing north, after a while the rotating pairs are oriented in different directions. We can now lock the rotation speed of the dancers to the direction they move. This results in a perfect choreography where all the women in a certain area face the same direction. This control and ability to manipulate and observe the spin is an important step in the development of spin-based transistors that are electrically programmable."
How it Works
IBM scientists used ultra short laser pulses to monitor the evolution of thousands of electron spins that were created simultaneously in a very small spot. Atypically, where such spins would randomly rotate and quickly loose their orientation, for the first time, the scientists could observe how these spins arrange neatly into a regular stripe-like pattern, the so-called persistent spin helix.
The concept of locking the spin rotation was originally proposed in theory back in 2003 and since that time some experiments have even found indications of such locking, but until now it had never been directly observed.
IBM scientists imaged the synchronous 'waltz' of the electron spins by using a time-resolved scanning microscope technique. The synchronization of the electron spin rotation made it possible to observe the spins travel for more than 10 micrometers or one-hundredth of a millimeter, increasing the possibility to use the spin for processing logical operations, both fast and energy-efficiently.
The reason for the synchronous spin motion is a carefully engineered spin-orbit interaction, a physical mechanism that couples the spin with the motion of the electron. The semiconductor material called gallium arsenide (GaAs) was produced by scientists at ETH Zurich who are known as world-experts in growing ultra-clean and atomically precise semiconductor structures. GaAs is a III/V semiconductor commonly used in the manufacture of devices such as integrated circuits, infrared light-emitting diodes and highly efficient solar cells.
Transferring spin electronics from the laboratory to the market still remains a major challenge. Spintronics research takes place at very low temperatures at which electron spins interact minimally with the environment. In the case of this particular research IBM scientists worked at 40 Kelvin (-233 C, -387 F).
This work was financially supported by the Swiss National Science Foundation through National Center of Competence in Research (NCCR) Nanoscale Sciences and NCCR Quantum Science and Technology.
The scientific paper entitled "Direct mapping of the formation of a persistent spin helix" by M.P. Walser, C. Reichl, W. Wegscheider and G. Salis was published online in Nature Physics, DOI 10.1038/NPHYS2383 (12 August 2012).
