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New kind of magnetism discovered: ’Quantum Spin Liquid’ 2012-12-24 0:00
Following up on earlier theoretical predictions, MIT researchers have now demonstrated experimentally the existence of a fundamentally new kind of magnetic behavior, adding to the two previously known states of magnetism.
Ferromagnetism -- the simple magnetism of a bar magnet or compass needle -- has been known for centuries. In a second type of magnetism, antiferromagnetism, the magnetic fields of the ions within a metal or alloy cancel each other out. In both cases, the materials become magnetic only when cooled below a certain critical temperature. The prediction and discovery of antiferromagnetism -- the basis for the read heads in today’s computer hard disks -- won Nobel Prizes in physics for Louis Neel in 1970 and for MIT professor emeritus Clifford Shull in 1994.
"We’re showing that there is a third fundamental state for magnetism," says MIT professor of physics Young Lee. The experimental work showing the existence of this new state, called a quantum spin liquid (QSL), is reported this week in the journal Nature, with Lee as the senior author and Tianheng Han, who earned his PhD in physics at MIT earlier this year, as lead author.
MIT physicists grew this pure crystal of herbertsmithite in their laboratory. This sample, which took 10 months to grow, is 7 mm long (just over a quarter-inch) and weighs 0.2 grams.
The QSL is a solid crystal, but its magnetic state is described as liquid: Unlike the other two kinds of magnetism, the magnetic orientations of the individual particles within it fluctuate constantly, resembling the constant motion of molecules within a true liquid.
Finding the evidence
There is no static order to the magnetic orientations, known as magnetic moments, within the material, Lee explains. "But there is a strong interaction between them, and due to quantum effects, they don’t lock in place," he says.
Although it is extremely difficult to measure, or prove the existence, of this exotic state, Lee says, "this is one of the strongest experimental data sets out there that [does] this. What used to just be in theorists’ models is a real physical system."
Philip Anderson, a leading theorist, first proposed the concept in 1987, saying that this state could be relevant to high-temperature superconductors, Lee says. "Ever since then, physicists have wanted to make such a state," he adds. "It’s only in the past few years that we’ve made progress."
The material itself is a crystal of a mineral called herbertsmithite. Lee and his colleagues first succeeded in making a large, pure crystal of this material last year -- a process that took 10 months -- and have since been studying its properties in detail.
"This was a multidisciplinary collaboration, with physicists and chemists," Lee explains. "You need both … to synthesize the material and study it with advanced physics techniques. Theorists were also crucial to this."
Through its experiments, the team made a significant discovery, Lee says: They found a state with fractionalized excitations, which had been predicted by some theorists but was a highly controversial idea. While most matter has discrete quantum states whose changes are expressed as whole numbers, this QSL material exhibits fractional quantum states. In fact, the researchers found that these excited states, called spinons, form a continuum. This observation, they say in their Nature paper, is "a remarkable first."
Obama Arms ISIS-Linked Militants, Pushes Gun Control On Very Same Day 2015-10-07 6:19
President Obama authorized a shipment of guns to the Syrian opposition, a.k.a. ISIS-linked militants, on the exact same day he demanded more gun control in response to the Oregon shooting.
Even more shocking, Obama did the very same thing after the 2013 D.C. Navy Yard shooting.
The president approved the re-arming of the Syrian opposition, which predominantly consists of ISIS and its ...
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Colleagues are alleged to have said that reporting the crime would set back their struggle for a borderless world.
The ‘No Borders’ activist had dedicated a month of her life to helping migrants. Her group was stationed between Italy and France in Ponte San Ludovico in Ventimiglia when the atrocity occurred, according to reports from local papers La Stampa and Il Secolo XIX, ...
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A Dutch Muslim politician has called for a ban on dogs in The Hague, the third-largest city in the Netherlands.
Islamic legal tradition holds that dogs are "unclean" animals, and some say the call to ban them in Holland and elsewhere represents an attempted encroachment of Islamic Sharia law in Europe.
This latest canine controversy -- which the Dutch public has greeted ...
Islamic State 'blows up Palmyra arch' 2015-10-06 21:37
Palmyra's Arch of Triumph was built by the Romans in the second Century AD
Islamic State militants in northern Syria have blown up another monument in the ancient city of Palmyra, officials and local sources say.
The Arch of Triumph was "pulverised" by the militants who control the city, a Palmyra activist told AFP news agency.
It is thought to have been ...