IBM’s Waltzing Electrons Promise Spintronics Memory Breakthrough

IBM scientists have published research that shows how a technique called “spintronics” may lead to lower-energy memory, with a much greater storage density.

Using electrons’ spin to store information has been a cherished idea for some time, as it could lead to vast storage density – essentially treating groups of electrons as magnetic domains far tinier than those in conventional magnetic media. Scientists from IBM and the ETH Zurich University have produced images which prove that these spins can be made persistent enough to store data – but there are still many hurdles to overcome before spintronics devices become a reality.

Strictly spintronics

While conventional electronics is based on flows of charges, spintronics moves to a property which can be addressed at a smaller level – the spin of the electron itself – and which would require less energy to operate.

Researchers have already found a “persistent spin helix” can be produced in  zincblende semiconductors, and preserved for comparatively long times. These times are in fact only nanoseconds, so they are only persistent from the point of view of a processor operating at GHz frequencies.

The proof that these states persist and can be maznipulated has come from a paper in Nature Physics by IBM scientists  Matthias Walser and Gian Salis (in picture), working with C. Reichl and W. Wegscheider of the Solid State Physics Laboratory of the ETH Zurich University.

The team succeeded in creating a direct mapping of a local spin excitation, evolving into a persistent spin helix, and shoing how it interacts with an external magnetic field. This is important as the external field would be used to set and read the state of the spintronics bits.

The trick to preserving a coherent spin is to get a set of electrons spinning and moving together, which Dr Salis likens to couples dancing a Viennese waltz:  “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.”

The team used ultra short laser pulses to monitor the evolution of thousands of electron spins that were created simultaneously in a very small spot. The spins can arrange neatly into regular stripes, which are referred to as the persistent spin helix, and this was observed using a time-resolved scanning microscope technique.

The helix was seen to move by more than 10 micrometers or one-hundredth of a millimeter, and persist long enough to use for energy-efficient data processing and storage, say the researchers. Synchronising the spin with this movement is the trick to getting the helix to remain persistent.

Some serious barriers still remain to using this technique commercially. In particular the researchers have been working at a temperature only 40 degrees above absolute zero (40K or -233C).

“Direct mapping of the formation of a persistent spin helix” by M.P. Walser, C. Reichl, W. Wegscheider and G. Salis is published online in Nature Physics, DOI 10.1038/NPHYS2383 (12 August 2012).

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