From: Mustafa Akgul (akgul@Bilkent.EDU.TR)
Date: Fri 15 Aug 2003 - 17:02:33 EEST
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Tarih: 15 Aug 2003 17:10 EEST
Kimden: HPCwire <hpcwire@tgc.com>
Konu: 105730 "SPINTRONICS" COULD ENABLE FUTURE ELECTRONIC DEVICES 08.15.03
"SPINTRONICS" COULD ENABLE FUTURE ELECTRONIC DEVICES 08.15.03
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Moore's Law - a dictum of the electronics industry that says the number of
transistors that fit on a computer chip will double every 18 months - may soon
face some fundamental roadblocks. Most researchers think there'll eventually
be a limit to how many transistors they can cram on a chip. But even if
Moore's Law could continue to spawn ever-tinier chips, small electronic
devices are plagued by a big problem: energy loss, or dissipation, as signals
pass from one transistor to the next. Line up all the tiny wires that connect
the transistors in a Pentium chip, and the total length would stretch almost a
mile. A lot of useful energy is lost as heat as electrons travel that
distance.
Theoretical physicists at Stanford and the University of Tokyo think they've
found a way to solve the dissipation problem by manipulating a neglected
property of the electron - its "spin," or orientation, typically described by
its quantum state as "up" or "down." They report their findings in the Aug. 7
issue of Science Express, an online version of Science magazine. Electronics
relies on Ohm's Law, which says application of a voltage to many materials
results in the creation of a current. That's because electrons transmit their
charge through the materials. But Ohm's Law also describes the inevitable
conversion of electric energy into heat when electrons encounter resistance as
they pass through materials.
"We have discovered the equivalent of a new 'Ohm's Law' for spintronics - the
emerging science of manipulating the spin of electrons for useful purposes,"
says Shoucheng Zhang, a physics professor at Stanford. Professor Naoto Nagaosa
of the University of Tokyo and his research assistant, Shuichi Murakami, are
Zhang's co-authors. "Unlike the Ohm's Law for electronics, the new 'Ohm's Law'
that we've discovered says that the spin of the electron can be transported
without any loss of energy, or dissipation. Furthermore, this effect occurs at
room temperature in materials already widely used in the semiconductor
industry, such as gallium arsenide. That's important because it could enable a
new generation of computing devices."
Zhang uses a celestial analogy to explain two important properties of
electrons - their center of mass and their spin: "The Earth has two kinds of
motion. One is that its center of mass moves around the Sun. But the other is
that it also spins by itself, or rotates. The way it moves around the Sun
gives us the year, but the way it rotates around by itself gives us the day.
The electron has similar properties." While electronics uses voltage to move
an electron's center of mass, spintronics uses voltage to manipulate its spin.
The authors predict that application of an electric field will cause
electrons' spins to flow together collectively in a current. The applied
electric force, the spins and the spin current align in three different
directions that are all perpendicular to each other (see film of the effect at
http://news-service.stanford.edu/news/2003/august20/zhang-video-820.html).
"This is a remarkable thing," explains Zhang. "I push you forward and you move
sideways - not in the direction that I'm pushing you."
So far, only superconductors are known to carry current without any
dissipation. However, extremely low temperatures, typically -150 degree
Celsius, are required for the dissipationless current to flow inside a
superconductor. Unlike electronic superconductors being investigated in
advanced laboratories throughout the world, whose operating temperatures are
too low to be practical in commercial devices, Zhang, Nagaosa and Murakami
theorize that the dissipationless spin current will flow even at room
temperature.
"This [the work reported in the paper] is a theoretical prediction," Zhang
says. "The next step is to work closely with experimental labs to verify this
prediction and to demonstrate this effect." That will require creating
materials and testing them with a sensitive spin detector. "Once this is done
we can go ahead to propose different device structures which take advantage of
this effect," he says.
Zhang characterizes his work as fundamental research but says spintronics is
already making its way into devices in other labs. With lack of dissipation,
spintronics may be the best mechanism for creating ever-smaller devices. The
potential market is enormous, he says. "In maybe a 10-year timeframe,
spintronics will be on par with electronics," he predicts. "That's why there's
a huge race going on around the world."
The National Science Foundation and the Department of Energy in the United
States and the Ministry of Education, Culture, Sports, Science and Technology
in Japan funded the work.
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