Ohm’s Law calculates how many electrons will begin to move in a wire or transistor when a battery or other voltage source is applied at each end. It also determines how much energy is ultimately lost as waste heat during such electron forward motion. This excess heat loss provides practical limits on how small a device can be made before it melts and is the primary limitation on making smaller and smaller computer chips.
Zhang’s team has discovered that applying a voltage can 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 in the transporting material; the effect is illustrated in a movie produced by Zhang. “This is a remarkable thing,” explains Zhang. “I push you forward and you move sideways — not in the direction that I’m pushing you.”
Electron spin transport by Zhang’s method occurs without energy loss or generation of waste heat, and so it may be used to create electronic devices much smaller and without the overheating problems that plague today’s electronics. 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.
Zhang’s team reports their findings in the Aug. 7 issue of Science Express, an online version of Science magazine.
“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.”
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