New kind of magnetism discovered: Experiments demonstrate 'quantum spin liquid'

Dec 20, 2012 by David Chandler
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. Image: Tianheng Han

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.

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."

Scattering neutrons

To measure this state, the team used a technique called neutron scattering, which is Lee's specialty. To actually carry out the measurements, they used a neutron spectrometer at the National Institute of Standards and Technology (NIST) in Gaithersburg, Md.

The results, Lee says, are "really strong evidence of this fractionalization" of the spin states. "That's a fundamental theoretical prediction for spin liquids that we are seeing in a clear and detailed way for the first time."

It may take a long time to translate this "very fundamental research" into practical applications, Lee says. The work could possibly lead to advances in data storage or communications, he says—perhaps using an exotic quantum phenomenon called long-range entanglement, in which two widely separated particles can instantaneously influence each other's states. The findings could also bear on research into high-temperature superconductors, and could ultimately lead to new developments in that field, he says.

"We have to get a more comprehensive understanding of the big picture," Lee says. "There is no theory that describes everything that we're seeing."

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User comments : 12

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Maggnus
2.3 / 5 (12) Dec 20, 2012
oh oh, the word "magnetism" is in the title. Expect the EU nuts to comment in 3 - 2 -
ChrisKeturakis
1 / 5 (2) Dec 20, 2012
This is about the exact same research as another article published today on physorg: http://phys.org/n...ity.html

Are we trying to give MIT double the publicity?

Lurker2358
2 / 5 (7) Dec 20, 2012
This is about the exact same research as another article published today on physorg: http://phys.org/n...ity.html

Are we trying to give MIT double the publicity?


So what?

Two different contributors wrote about the same topic because it happened to interest them most. It happens all the time with news and weather.
ValeriaT
1.8 / 5 (5) Dec 20, 2012
Nature article. Herbertsmithite is zinc-copper oxychloride, something similar to blue stone and it has transparent blue-green color. The sample pictured above looks like partially dehydrated crystal being covered with anhydrous cupric chloride.
extinct
1.8 / 5 (5) Dec 20, 2012
in the 5th paragraph, the comma should've been after "of" and not before it
Infinion
2.5 / 5 (8) Dec 20, 2012
Maggnus, how does this have anything to do with EU theory?

It's pretty easy to know when proponents of EU theory [EU nuts] will post in articles.

1)Astronomy articles that talk about gas, filamentary structures, sources of x-rays, black hole jets, or the cause of magnetic fields will have CantDrive85 or HannesAlfven posting to correct the semantics of the article based on EU theory, or condemning theoretical physicists for misinterpreting the phenomena based on mainstream theories or for not taking evidence into account that would otherwise support electrical activity in space.

2)Articles like this one in physics are [more often than not] based on empirical laboratory evidence from experiments, the best kind. EU proponents believe the model being used to falsify theories in astronomy, on the other hand, are deductively invalid. I.e they believe that because scientific method excludes the interaction of one of the fundamental forces in nature, the phenomena is misinterpreted
Infinion
2.5 / 5 (8) Dec 20, 2012
and they further believe that because the phenomena is misinterpreted, it leads to a broader misunderstanding in further observations.

I don't really agree with how CantDrive85 and HannesAlfven argue this point by constantly correcting Physorg articles or condemning theoretical physicists and then posting a link to the thunderbolts website to solidify their 'argument'. They need to realize that they lose a lot of credence this way, and people will very quickly tune out the same story they make over and over again.

But I digress, Real EU proponents adhere to logical positivism -- their ideas require both empiricism and mathematical rationalism.

The ones here on Physorg just have a serious problem giving strong reasons or evidence to accept their particular conclusion, which is why they post links to do it for them.
Maggnus
3.2 / 5 (9) Dec 20, 2012
@ Infinion; my tongue in cheek comment was aimed at exactly the people you are attempting to defend. I have been hearing about the EU idea since about 98, and in that time I have seen all manner of articles hijacked by the eu crowd simply because the article had a word in it related to magnetism.

And "real EU proponants" is an oxymoron. The "real" proponants are mostly dead, or have come to the realization that the whole idea was wrong. The only proponants left are those who do not understand the very theory they think they are promoting.
cantdrive85
1 / 5 (8) Dec 20, 2012
Hot gas.
axemaster
5 / 5 (6) Dec 20, 2012
"We're showing that there is a third fundamental state for magnetism," says MIT professor of physics Young Lee.


Ah this is epic! I helped him run 8.01L (undergraduate mechanics) this semester!

He's a super cool guy, insults shall NOT be tolerated!
Macksb
2.6 / 5 (5) Dec 20, 2012
I posted my comments following the other article about the exact same research, as identified above by ChrisKeturakis. I agree with Axemaster...epic, cool work as one would expect from MIT. See my comments following the other article, if interested.
Horus
1 / 5 (1) Dec 21, 2012
in the 5th paragraph, the comma should've been after "of" and not before it


The comma should have been removed. From:

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.''

to:

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.''

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