Way to Control Electron Spin with Electrical Field

The race for smaller, faster, and more powerful computers and consumer electronics took a new spin as researchers at the University of Pittsburgh and the University of California at Santa Barbara (UCSB) became the first to control electrons using electrical, rather than magnetic, fields.

In its Jan. 23 edition, Science Express, the online portal of the magazine Science, published a report on the breakthrough of Jeremy Levy and David Awschalom. Levy is an associate professor of physics and astronomy at Pitt and director of its Center for Oxide-Semiconductor Materials for Quantum Computing (http://cosmqc.net). Awschalom is a professor of physics and electrical and computing engineering at UCSB and director of its Center for Spintronics and Quantum Computation, part of the California NanoSystems Institute.

The breakthrough is important in that it demonstrates that spin-based technologies, or spintronics, are compatible with technologies used in today's electronics and moves the esoteric fields of spintronics and quantum computing closer to reality.

Electrons, the basic particles of electricity, are negatively charged particles that encircle the nuclei of all atoms. Electrons can move to produce electrical currents, but they also spin about their own axes, which can point either up or down. This spin creates a small magnetic field that can be affected by other magnetic fields.

Levy and Awschalom's breakthrough opens the possibility of using the spin orientation of electrons to store information, much in the same way that the open and closed states of electrical switches store information in computers and many other electronic devices.

Scientists have been able to manipulate electron and nuclear spin with magnetic fields. For example, in magnetic resonance imaging, rapidly alternating magnetic fields can control electron and nuclear spins in three dimensions. However, magnetic fields are far more difficult to generate and control on a smaller scale. Levy and Awschalom realized that if they designed a structure for which the axis of the spin could be manipulated using an applied electrical field, the spin direction itself could be changed."Most researchers using the spin-based model for spintronics and quantum computing have assumed that the behavior of spins must be controlled by magnetic fields," said Levy. "The prospect of controlling 100 million magnets each independently on the equivalent of [the size of] a chip has boggled the imagination of researchers. However, with electrical gates, we already control 100 million devices in modern computers."

Aschwalom's graduate student constructed a semiconductor of aluminum gallium arsenide and gallium arsenide, flanked by metal plates. When they applied microwave electrical signals to the plates, the researchers were able to change the spin of the electrons.

The plates used in the researchers' experiments were 50 microns wide, and the tests were done at a low temperature, but Levy and Aschwalom say it will not be difficult to design smaller chips to operate at higher temperatures.

Funding for the project is being provided by the Defense Research Project Agency.