Thursday, July 17, 2008

Discovery by UC Riverside physicists could enable development of faster computers

Ferromagnet Semiconductor Structure

Caption: Sketch of a ferromagnet/semiconductor structure. When the MgO interface is very thin, spin up electrons, represented in this image with an arrow to the right, are reflected back to the semiconductor. At an intermediate thickness of the interface, spin down electrons are reflected back to the semiconductor, resulting in a "spin reversal" that can be used to control current flow. Credit: Kawakami lab, UC Riverside. Usage Restrictions: None.
Roland Kawakami's lab proposes a simple technique for controlling electron spin and current flow.

RIVERSIDE, Calif. – Physicists at UC Riverside have made an accidental discovery in the lab that has potential to change how information in computers can be transported or stored. Dependent on the "spin" of electrons, a property electrons possess that makes them behave like tiny magnets, the discovery could help in the development of spin-based semiconductor technology such as ultrahigh-speed computers.
The researchers were experimenting with ferromagnet/semiconductor (FM/SC) structures, which are key building blocks for semiconductor spintronic devices (microelectronic devices that perform logic operations using the spin of electrons). The FM/SC structure is sandwich-like in appearance, with the ferromagnet and semiconductor serving as microscopically thin slices between which lies a thinner still insulator made of a few atomic layers of magnesium oxide (MgO).
Flow of Electrons Based on their Spin

Caption: Sketch shows how the thickness of the magnesium oxide interface enables a "spin reversal" in electrons traveling through the interface. The interface is depicted as a yellow wall here. Credit: Kawakami lab, UC Riverside. Usage Restrictions: None.
The researchers found that by simply altering the thickness of the MgO interface they were able to control which kinds of electrons, identified by spin, traveled from the semiconductor, through the interface, to the ferromagnet.

Study results appear in the June 13 issue of Physical Review Letters.
Experimental results:

The spin of an electron is represented by a vector, pointing up for an Earth-like west-to-east spin; and down for an east-to-west spin. Center for Nanoscale Science and Engineering, and Li were joined by UCR's Y. Chye, Y.F. Chiang, K. Pi and W. H. Wang; and UC Santa Barbara's J.M. Stephens, S. Mack and D.D. Awschalom.

Grants from the Office of Naval Research, the National Science Foundation and the Center for Nanoscience Innovation for Defense supported the two-year study.

The University of California, Riverside is a doctoral research university, a living laboratory for groundbreaking exploration of issues critical to Inland Southern California, the state and communities around the world. Reflecting California's diverse culture, UCR's enrollment of about 17,000 is projected to grow to 21,000 students by 2010. The campus is planning a medical school and already has reached the heart of the Coachella Valley by way of the UCR Palm Desert Graduate Center. With an annual statewide economic impact of nearly $1 billion, UCR is actively shaping the region's future. To learn more, visit or call (951) UCR-NEWS.

Contact: Iqbal Pittalwala 951-827-6050 University of California - Riverside

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