ZURICH – 12 Aug 2012: Aiming to use electron
spins for storing, transporting and processing information,
researchers from IBM (NYSE:IBM) and scientists at ETH
Zurich, a leading European university, today revealed the
first-ever direct mapping of the formation of a persistent spin
helix in a semiconductor.
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).
