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Nuclear spins make current in OLED stronger or weaker

Posted: 23 Sep 2014     Print Version  Bookmark and Share

Keywords:OLED  nuclear spin  current 

A team of physicists at the University of Utah discovered that data from readings of subatomic spins in the nuclei of hydrogen isotopes could be used to control the current powering light in a plastic LED—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, or OLEDs, more efficient than those used today in display screens for cell phones, computers and televisions.

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, explained 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 -234.4°C (nearly absolute zero), was bombarded with intense microwaves and exposed to superstrong magnetic fields.

In the new 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, said Boehme.

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, explained Boehme.

Harnessing nuclear spins can increase the efficiency of electronic materials out of which so much technology is made, said Boehme. 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 Center, funded by the National Science Foundation.

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. The 2010 study by Boehme and colleagues showed that nuclear spins of phosphorus in a silicon semiconductor could control electrical current, but at impractically low temperatures and strong magnetic fields. They had to use the magnetic fields to align spins of phosphorus electrons in the same direction, and then use intense light to transfer the same alignment to the spins of phosphorus nuclei. Then they bombarded the semiconductor with radio waves to reverse the nuclear spins and control the current.

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