KU News Release


March 7, 2011
Contact: Brendan M. Lynch, University Relations, 785-864-8855

For first time, researchers detect the curving flight of a spinning electron

LAWRENCE — Imagine a major league pitcher such as Pedro Martinez throwing a curveball for a strikeout, or a soccer star like David Beckham arcing a ball past a goalie. Both the baseball and soccer ball can bend through the air because both are spinning.

So, consider how a spinning electron might behave within solid material.

For years, physicists have predicted that electrons too would curve through solid materials because every electron spins either clockwise or counterclockwise. The problem has been that — because they are so small and speedy — the curving electrons have been impossible to observe.

Now, one scientist has made that breakthrough. Hui Zhao, assistant professor of physics and astronomy at the University of Kansas, has confirmed that spinning electrons curve as they pass through a semiconductor. His paper, co-authored by KU graduate students Lalani Werake and Brian Ruzicka, will appear in a forthcoming issue of Physical Review Letters and an accompanying Physical Review Focus story.

“We invented a new ultrafast laser technique,” said Zhao. “It allows us to take a snapshot every 100 femtoseconds (100 millionth of one billionth of one second) with a resolution of 0.1 nanometer (0.1 billionth of one meter). So this can be viewed as an extremely high definition camera. It was not possible before this that you could watch an electron fly with such time and spatial resolution.”

During one experiment at KU’s Ultrafast Laser Lab, electrons moved sideways because of their spin by as much as 0.4 nanometers after traveling only 10 nanometers along the launched direction in 400 femtoseconds. The path of curve was tied to the spin direction of the electron.

“We immediately tried other two samples, just to make sure the observation was general,” Zhao said. “Once we convinced ourselves that this was true, we were very excited.”

The scientists’ verification that electrons curve, a phenomenon dubbed the “spin Hall effect,” will impact the emerging field of spintronics.

Today’s extreme miniaturization of microchip technology has bumped up against natural limits — their transistors simply can’t get much smaller — so spintronics promises a way to develop tomorrow’s faster and more efficient computers. The technology uses the spin direction of electrons to express the ones and zeros that comprise digital data.

“For the last 50 years, we’ve made each electronic device smaller and smaller, so that we can put a larger and larger number of devices on a silicon chip, called an integrated circuit,” said Zhao. “Now the size of each device is around 50 nanometers. There’s not much room to shrink this down any further. We cannot play this trick again, so we need an entirely new technology to make our electronics and computers more powerful.”

The curving effect of spinning electrons, now confirmed, could point the way to better detection and generation of spin currents in nanoscale devices and eventually more robust computers. In fact, the cutting-edge research at Zhao’s Ultrafast Laser Lab will now focus on how electrons behave in materials that have more commercial applications.

“We want to extend this research to silicon, and other materials that are more relevant, because the whole semiconductor industry is based on silicon,” Zhao said.

A five-year CAREER Award from the National Science Foundation supported the research.


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