For the first time IBM scientists have observed how electron spins move tens of micrometers in a semiconductor channel, with their orientations synchronously rotating along the path similar to a couple dancing the waltz, the famous Viennese ballroom dance. This is spinhelix rendering of the phenomenon. |
Aiming
to use electron spins for storing, transporting and processing
information, researchers from 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 nanosec—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.
In this photo, IBM scientists Matthias Walser (left) and Gian Salis who published the finding with C. Reichl and W. Wegscheider from ETH Zurich in the August 12, 2012 online edition of Nature Physics. |
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.
Direct mapping of the formation of a persistent spin helix
Source: IBM Research
