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'Third state of magnetism' could advance storage, superconducting

Diana Scheben -January 29, 2013

A multidisciplinary team at the Massachusetts Institute of Technology claims to have demonstrated the existence of a long-theorized state of magnetism, called quantum spin liquid (QSL), that could have eventual application in computer memory storage and high-temperature superconductors. QSL is a solid crystal, but the fluctuating magnetic orientations of its individual particles resemble the constant motion of molecules within a liquid.

“We’re showing that there is a third fundamental state for magnetism” in addition to ferromagnetism and anti-ferromagnetism, says MIT physics professor Young Lee, senior author of a paper on the work that appeared in the Dec 20, 2012, issue of Nature (Fractionalized excitations in the spin-liquid state of a kagome-lattice antiferromagnet). There is no static order to the magnetic moments (orientations) within the material, “but there is a strong interaction between them, and due to quantum effects they don’t lock in place,” Lee adds.

MIT physicists grew this pure crystal of herbertsmithite in their lab over a span of 10 months. The sample measures 7 mm long and weighs 0.2g (courtesy Tian-Heng Han).

The existence of QSLs has been theorized since 1987 but has been difficult to prove. MIT researchers spent 10 months growing a pure crystal of a suspected QSL material, herbertsmithite, and used a neutron spectrometer at the National Institute of Standards and Technology in Gaithersburg, MD, to analyze the material’s structure through neutron scattering.

In their experiments on the crystal, the team found a state with fractionalized excitations; those excited states, called spinons, formed a continuum. “That’s a fundamental theoretical prediction for spin liquids that we are seeing in a clear and detailed way for the first time” through the team’s fundamental research, says Lee.

Practical results are a long ways off, but the work could lead to advances in data storage or communications, perhaps using long-range quantum entanglement.

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