Physicists Devise Viable Design For Spin-Based Electronics
at the University of California, San Diego have proposed a design for a semiconductor computer circuit based on the spin of electrons. They say the device would be more scalable and have greater computational capacity than conventional silicon circuits.
The “spintronic”—or spin-based electronic—device, described this week in the journal Nature, would extend the scope of conventional electronics by encoding information with the magnetic—or spin—state of electrons, in addition to the charge of the electrons. The researchers used a novel geometry to overcome the weakness of the magnetic signal, the current limitation to developing spintronics in silicon semiconductors.
“The breakthrough of our research is the device geometry, the way it is activated, and the way it could be integrated in electronic circuits,” said Lu J. Sham, a professor of physics at UCSD and the senior author on the paper. “All of these features are novel and our results show for the first time a spin-based semiconductor circuit.”
One advantage of spintronics is that it shrinks the size of the circuit that is needed to perform a given logic operation. The researchers say that their proposed device has other important advantages compared with conventional electronics.
“Spin-based electronic devices allow the construction of reprogrammable circuits without hindering performance,” explained Hanan Dery a postdoctoral fellow working with Sham and the lead author on the paper. “This will allow flexible electronic devices which fit into any application while providing the best performance. For example, the same circuit can serve as i-Pod, cellular phone, microprocessor, et cetera.”
The proposed spintronic circuit is an interconnected series of logic gates. Each logic gate consists of five magnetic contacts lying on top of a semiconductor layer. The magnetic state of each of these contacts, determined by the electrons’ spins, corresponds to the “0” and “1” in each bit of information. The logic operation is performed by moving electrons between four of the magnetic contacts and the semiconductor. The result of the operation is read by the fifth magnetic contact.
The proposed device has not yet been made, but according to the researchers it should be feasible with currently available technology.
New Development in Spintronics: Spin-polarized Electrons OnDemand, With A Single Electron Pump
ScienceDaily (Jan. 21, 2009) — Many hopes are pinned on spintronics. In the future it could replace electronics, which in the race to produce increasingly rapid computer components, must at sometime reach its limits. Different from electronics, where whole electrons are moved (the digital "one" means "an electron is present on the component", zero means "no electron present"), here it is a matter of manipulating a certain property of the electron, its spin.
Schematic. The goal of spintronics (also called spin electronics) is to systemically control and manipulate single spins in nanometer-sized semiconductor components in order to thus utilize them for information processing. (Credit: A. Müller, PTB)
For this reason, components are needed in which electrons can be injected successively into the electron, and one must be able to manipulate the spin of the single electrons, e.g. with the aid of magnetic fields. Both are possible with a single electron pump, as scientists of the Physikalisch-Technische Bundesanstalt (PTB) in Germany have, together with colleagues from Latvia, now shown.
Electrons can do more than be merely responsible for current flow and digital information. If one succeeds in utilizing their spin, then many new possibilities would open up. The spin is an inner rotational direction, a quantum-mechanical property which is shown by a rotation around its own axis. An electron can rotate counterclockwise or clockwise. This generates a magnetic moment. One can regard the electron as a minute magnet in which either the magnetic North or South Pole "points upwards" (spin-up or spin-down condition). The electronic spins in a material determine its magnetic properties and are systematically controllable by an external magnetic field.
This is precisely the goal of spintronics (also called spin electronics): systemically control and manipulate single spins in nanometer-sized semiconductor components in order to thus utilize them for information processing. This would even have several advantages: The components would be clearly faster than those that are based on the transport of charges. Furthermore, the process would require less energy than a comparable charge transfer with the same information content. And with the value and direction of the expected spin value, further degrees of freedom would come into play, which could be used additionally for information representation.
In order to be able to manipulate the spins for information processing, it is necessary to inject the electrons singly with predefined spin into a semiconductor structure. This has now been achieved by researchers of the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig and the University of Latvia in Riga. In the current issue of the physics journal Applied Physics Letters, they present investigations of a so-called single electron pump. This semiconductor device allows the ejection of exactly one single electron per clock cycle into a semiconductor channel.
In the measurements presented it was shown for the first time that such a single electron pump can also be reliably operated in high magnetic fields. For sufficiently high applied fields, the pump then delivers exactly one single electron with predefined spin polarization per pumping cycle. It thus delivers spin-polarized electrons virtually on demand. The robust design and the high achievable clock rate in the gigahertz range makes such a spin-polarized single electron pump a promising candidate especially also for future spintronic applications
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