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Subatomic spins control current in plastic LEDs

Posted: 24 Sep 2014 ?? ?Print Version ?Bookmark and Share

Keywords:University of Utah? LED? spintronics? hydrogen isotope? OLED?

A team of physicists at the University of Utah has read the subatomic "spins" in the centres or nuclei of hydrogen isotopes, and used the data to control current that powered light in a cheap, plastic LED. They were able to do this at room temperature and without strong magnetic fields.

The study, published in the journal Science, brings physics a step closer to practical machines that work "spintronically" as well as electronically: superfast quantum computers, more compact data storage devices and plastic or organic light-emitting diodes (OLEDs), more efficient than those used today in display screens for cell phones, computers and TVs.

"We have shown we can use room-temperature, plastic electronic devices that allow us to see the orientation of the tiniest magnets in nature, the spins in the smallest atomic nuclei," stated physics professor Christoph Boehme, one of the study's principal authors. "This is a step that may lead to new ways to store information, produce better displays and make faster computers."

The experiment is a much more practical version of a study Boehme and colleagues published in Science in 2010, when they were able to read nuclear spins from phosphorus atoms in a conventional silicon semiconductor. But they could only do so when the apparatus was chilled to minus 453.9°F (nearly absolute zero), was bombarded with intense microwaves and exposed to superstrong magnetic fields.

In the experiments, the physicists were able to read the nuclear spins of two isotopes of hydrogen: a single proton and deuterium, which is a proton, neutron and electron. The isotopes were embedded in an inexpensive plastic polymer or organic semiconductor named MEH-PPV, an OLED that glows orange when current flows.

The researchers flipped the spins of the hydrogen nuclei to control electrical current flowing though the OLED, making the current stronger or weaker. They did it at room temperature and without powerful light bombardment or magnetic fields, in other words, at normal operating conditions for most electronic devices, Boehme said.

"This experiment is remarkable because the magnetic forces created by the nuclei are millions of times smaller than the electrostatic forces that usually drive currents," yet they were able to control currents, he indicated.

Harnessing nuclear spins can increase the efficiency "of electronic materials out of which so much technology is made," Boehme added. "It also raises the question whether this effect can be used for technological applications such as computer chips that use nuclear spins as memory and our method as a way to read the spins."

The U.S. Department of Energy funded the study, and the physicists used facilities of the University of Utah's Materials Research Science and Engineering Centre, funded by the National Science Foundation.

Boehme conducted the study with fellow University of Utah physicists: first author and postdoctoral fellow Hans Malissa; research professor and co-senior author John Lupton, who also is on the faculty of the University of Regensburg, Germany; distinguished professor Z. Valy Vardeny; professor Brian Saam; graduate students Marzieh Kavand and David Waters; and postdoctoral fellow Kipp van Schooten. Another co-author was Paul Burn of Australia's University of Queensland.

Electronic devices use electrical current or electrons, which are negatively charged particles orbiting the nuclei or centres of atoms. Modern computers store data electronically: data are stored as binary "bits" in which zero is represented by "off," or no electrical charge, and one is represented by "on" or the presence of electrical charge.

In spintronics, data are stored by the spins of either electrons or, preferably, atomic nuclei. Spin often is compared with a tiny bar magnet like a compass needle, either pointing up or down, representing one or zero, in an electron or an atom's nucleus. Nuclear spin orientations live longer, so are better for storing data.

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