BATON ROUGE – John F. DiTusa, professor of physics and astronomy at LSU, and his international colleagues have discovered an unusual magnetic material that behaves very differently from the average refrigerator magnet. He recently co-authored an article with researchers from around the world, titled, “Mesoscopic Phase Coherence in a Quantum Spin Fluid.” Their findings will be published in the prestigious Science magazine.
The results of their research have strong implications for the design of devices and materials for quantum information processing.
The group’s main goal was to demonstrate string order – also called quantum phase coherence – and to determine the factors affecting the ability to maintain this property over a finite distance. In order to investigate this, DiTusa, together with an international team of researchers, looked at a quantum spin liquid, a system where electron spins are coupled, but point in random directions. These spins can be thought of as atomic-sized bar magnets that point in random arrangements, which is in direct contrast to the behavior of household magnets, where the spins are mostly aligned. The material in which they discovered the quantum spin liquid is composed of chains of nickel-oxygen-nickel atoms.
The group found that the string order was maintained for relatively long distances, nearly 30 nanometers, or 100 times the distance between nickel atoms in the solid state, at temperatures close to absolute zero.
“I like to think of this novel state of matter as an orchestra without a conductor, each musician playing whatever comes to mind,” said DiTusa. “Though one trumpet player likes to play Jimmie Hendrix and an oboe player likes to play Bach, a miraculous occurrence takes place and, without realizing it, the entire room of musicians becomes locked into playing a Brahms symphony.”
In this case, DiTusa contends, the whole orchestra is acting as a single coherent entity, even though they are playing different parts of a nonexistent score. This coherence has a length scale of the size of the concert hall and lasts a time determined by the length of the symphony.
“In our nickel oxide magnet, although the individual nickel atoms don’t have spins that point all in the same direction, or even form a regularly repeating pattern, they all hang together to make a beautiful, coherent symphony,” he said.
Collaborators on this research include: Guangyong Xu of Johns Hopkins University and Brookhaven National Laboratory; Collin L. Broholm, Ying Chen and Michel Kenzelmann of Johns Hopkins University and the National Institute of Standards and Technology Center for Neutron Research; Yeong-Ah Soh of Dartmouth College; Gabriel Aeppli of the London Centre for Nanotechnology and University College of London; Christopher D. Frost from the ISIS Facility, Rutherford Appleton Laboratory, U.K.; Toshimitsu Ito and Kunihiko Oka of the National Institute of Advanced Industrial Science and Technology, or AIST, in Japan; and Hidenori Takagi, also from AIST and the University of Tokyo.
For more information, contact DiTusa at ditusa@phys.lsu.edu or 225-578-2606.
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