Stanford University

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EDITORS: The paper, “Dissipationless Quantum Spin Current at Room Temperature,” is posted on Science Express ( A movie of the effect can be downloaded at Courtesy: Shoucheng Zhang



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.


"This is a remarkable thing," explains Zhang. "I push you forward and you move sideways -- not in the direction that I'm pushing you."


"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."



By Dawn Levy
