TECHNOLOGY FOR CHANGE

Spintronics Breakthrough Harnesses Quantum Mechanics

R. Colin Johnson | Date: 11-06-09 | Comments

It's all in the spin: Researchers find the holy grail of spintronics, which will enable the whole semiconductor industry to transfer to a new paradigm.

Smarter electronic circuitry will, in the future, store information on the spin of an electron�up or down�rather than on the number of electrons stored, thereby saving energy, generating less heat and operating at higher speeds. Now University of Cincinnati researchers claim to have found spintronics' "holy grail"�electrical control of spin.

Today electronic devices store information�logical 1s and 0s�by charging up a storage component, such as a capacitor or a floating gate. Electronic charge accumulates in the storage device, raising its voltage until it rises from a 0 to a 1 (in a 5-volt system a 1 is encoded as 2.7 volts or above, and anything below 2.4 volts is a 0). Instead of storing electrical charge to encode a logical 1, as opposed to 0 (no charge), future spintronics devices will instead encode 1s and 0s as either the up or down spin of individual electrons.

Electrons have always had the intrinsic property of spin�either up of down�but as an effect of quantum mechanics it has been largely ignored. For instance, when charge is used to encode 1s and 0s, like today, the spin of the electrons stored is random. But by separating electrons by spin, and by controlling the spin state of individual electrons, data can be encoded as streams of electrons in the same spin state, rather than requiring thousands of electrons to accumulate as charge.

Unfortunately, controlling the spin of electrons is not easy. Since an electron's spin is associated with its magnetic moment, early attempts used ferromagnetic materials to filter electrons by spin state. Once separated, electrons in a known spin state can be metered out to encode information.

The holy grain of spintronics, however, is to take any electron as an input and change its spin to up or down under electrical control. Once achieved, such all-electric spintronics will enable the whole semiconductor industry to transfer to this new paradigm.

The researchers, led by professors Philippe Debray and Marc Cahay, made their first steps toward that goal by harnessing quantum confinement to flip an electron's spin orientation into the up state. First they fabricated in an indium-arsenide semiconductor a short quantum wire�called a quantum point contact�that constricted electrons as they pass through. Then by tuning the voltage potential of gates adjacent to the wire, the researchers were able to make one end of the wire more constricted than the other. Spin polarization was subsequently triggered by coupling to the spin-orbits of the electrons passing through the wire, an effect that was enhanced by Coulomb electron�electron interactions.

Their current prototype only outputs electrons in the "up" spin state, but for the future, the researchers plan to build spin-polarizers that can emit electrons in either the up or down spin state. Also, they plan to experiment with reproducing the circuit in gallium arsenide, a more mainstream material than the more temperamental indium arsenide.