Helix pattern is observed by prolonging life of electron spins to about the speed of a mobile processor clock pulse

So-called "zinc-blende" semiconductors (so named due to the zinc-like crystalline structure of III-V semiconductors, rather than the presence of elemental zinc) have seen growing use in recent years.  Materials like indium arsenide (InAs) and Gallium arsenide (GaAs) have been used in everything from lasers to thin-film solar cells due to their unique electrical properties.

I. In Search of a Spin

Now International Business Machines, Inc. (IBM) researchers working at a company-sponsored research center at the Eidgenössische Technische Hochschule Zürich -- or, ETH Zürich, as the college name is typically shortened  -- have managed to discover a new property of this special kind of semiconductor.  That property has allowed the team to achieve a major advance in spintronics, which could eventually take the storage/processing technology out of the lab and onto the market.

IBM describes the breakthrough in a press release, writing:

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."

IBM spintronics researcher
Left Image: IBM researchers Matthias Walser (left) and Gian Salis (right) pose next to their laboratory apparatus.  Righ Image: Professor Salis adjusts an instrument. [Source: IBM/ETH Zürich]

II. From the Lab to the Pocket: The Road Ahead

Electrons have two key traits -- motion (typically, rotation around an atom) and spin.  In a way they're like tiny planets orbitting their equivalent of the sun, in this regard.

Typically electrons rotate in a stochastic fashion, but researchers predicted in 2003 that some semiconductors' electrons could "spin lock" when exposed locally to a magnet field or massaged with laser pulses.  But the theorized phenomena had never been observed until now.

IBM's researchers managed to prolong the lifetime of the spins over 30 times using a purified GaAs semiconductor and carefully regulated interactions.  That was enough to allow the spins synchronizations to last 1.1 nanoseconds -- or about the speed of a modern smartphone CPU (1 GHz).

Taking advantage of the longer-lived spins the researchers observed the "persistent spin helix", a striped pattern of spin types, using a scanning electron microscope.  Spins were seen "waltzing" 10 um along the semiconductor.

Spin Helix
The spin-helix, as visualized by IBM engineers. [Image Source: IBM/ETH Zürich]

Spintronics could eventually offer subatomic replacements to both memory storage and processors.  

But despite the breakthrough and recent progress in the field, many hurdles remain to marketization.  One challenge is squeezing the lasers or micro-magnetics needed to control the spin onto tiny semiconductor devices.  

Another key hurdle is the temperature.  The IBM experiment was performed at a frigid 40 Kelvin (-233 C, -387 F).  That's colder than near-boiling liquid nitrogen, which is liquid at 77 K.

Liquid nitrogen
The spintronic experiment was performed at a temperature colder than the boiling point of liquid nitrogen. [Image Source: Friday Explosion]

Squeezing spintronics on the mobile devices of the future could give Moore's Law new life by catapaulting computer chips over the fundamental limits of atomic physics, into the realm of subatomics.  But figuring out how to chill a cell phone CPU to 40 K -- or alternatively how to coax the finnicky electronics to behave and more terrestial temperatures -- is a daunting task.

The paper on the work was published in the prestigious peer-reviewed journal Nature Physics.  The senior author was Gian Salis (IBM), while Matthias Walser (IBM) was the first author.  The paper's two other authors are Professor Werner Wegscheider (ETH  Zürich Physics) and Christian Reichl (ETH Zürich Physics Ph.D candidate), who contributed by growing the semiconductor specimens for IBM.

Sources: IBM, Nature

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