. 24/7 Space News .
Seeking moments of disorder
by Staff Writers
Santa Barbara CA (SPX) Sep 05, 2019

Artist's concept depicting magnetic moments having fluctuating alignments 120 degrees different from those of their neighbors.

The future of technology relies, to a great extent, on new materials, but the work of developing those materials begins years before any specific application for them is known. Stephen Wilson, a professor of materials in UC Santa Barbara's College of Engineering, works in that "long before" realm, seeking to create new materials that exhibit desirable new states.

In the paper "Field-tunable quantum disordered ground state in the triangular-lattice antiferromagnet NaYbO2," published in the journal Nature Physics, Wilson and colleagues Leon Balents, of the campus's Kavli Institute for Theoretical Physics, and Mark Sherwin, a professor in the Department of Physics, describe their discovery of a long-sought "quantum spin liquid state" in the material NaYbO2 (sodium ytterbium oxide).

The study was led by materials student Mitchell Bordelon and also involved physics students Chunxiao Liu, Marzieh Kavand and Yuanqi Lyu, and undergraduate chemistry student Lorenzo Posthuma, as well as collaborators at Boston College and at the U.S. National Institute of Standards and Technology.

At the atomic level, electrons in one material's lattice structure behave differently, both individually and collectively, from those in another material. Specifically, the "spin," or the electron's intrinsic magnetic moment (akin to an innate bar magnet) and its tendency to communicate and coordinate with the magnetic moments of nearby electrons differs by material.

Various types of spin systems and collective patterns of ordering of these moments are known to occur, and materials scientists are ever seeking new ones, including those that have been hypothesized but not yet shown to exist.

"There are certain, more classical moments that let you know to a very high degree of certainty that the spin is pointing in a particular direction," Wilson explained. "In those, the quantum effects are small. But there are certain moments where the quantum effects are large, and you can't precisely orient the spin, so there is uncertainty, which we call 'quantum fluctuation.'"

Quantum magnetic states are those in which the magnetism of a material is primarily driven by such quantum fluctuations, generally derived from the uncertainty principle, intrinsic to magnetic moments. "So, you envision a magnetic moment, but the uncertainty principle says that I can't perfectly orient that in any one direction," Wilson noted.

Explaining the quantum spin liquid state, which was proposed long ago and is the subject of this paper, Wilson said, "In conventional materials, the magnetic moments talk to one another and want to orient relative to one another to form some pattern of order." In classical materials, this order is disrupted by thermal fluctuations, what Wilson describes as "just heat from the environment."

"If the material is warm enough, it is nonmagnetic, meaning the moments are all sort of jumbled relative to one another," he explained. "Once the material is cooled, the moments start to communicate, such that their connection to one another outcompetes the thermal fluctuations and they form an ordered state. That's classical magnetism."

But things are different in the quantum world, and magnetic moments that fluctuate can actually be the inherent "ground state" of a material.

"So, you can ask if there is a magnetic state in which the moments are precluded from freezing or forming some pattern of long-range order relative to one another, not by thermal fluctuations, but instead, by quantum fluctuations," Wilson said.

"Quantum fluctuations become more relevant as a material cools, while thermal fluctuations increase as it heats up, so you want to find a magnet that doesn't order until you can get it cool enough such that the quantum fluctuations preclude it from ever ordering."

That quantum disorder is desirable because it is associated with entanglement, the quantum mechanical quality that makes it possible to encode quantum information. To determine whether NaYbO2 might exhibit that characteristic, the researchers had to determine the intrinsic, or ground state of the material's magnetic moments when all thermal fluctuations are removed.

In this particular system, Wilson was able to determine experimentally that the magnetic moments are intrinsically in a fluctuating, disordered state, thus confirming that a quantum disordered state exists.

To find the hypothesized state, said Wilson, "First you have to put highly quantum magnetic moments into a material, but your material needs to be constructed such that the moments don't want to order. You do that by using the principle of 'magnetic frustration.'"

A simple way to think of that, according to Wilson, is to imagine a single triangle in the lattice structure of the material. "Let's say I build my material so that the magnetic moments are all located on a triangular lattice," he said, "and they all talk to one another in a way that has them wanting to orient antiferromagnetically, or antiparallel, to one another."

In that arrangement, any adjacent moment on the triangle wants to orient antiparallel to its neighbor. But because there are an odd number of points, you have one up at one point and one down (antiparallel to the first) at the second point, meaning that the third moment has a differently oriented moment on each side, so it doesn't know what to do. All of the moments are competing with one another.

"That's magnetic frustration, and, as it turns out, it reduces the temperature at which the moments are finally able to find some arrangement they all agree on," Wilson said. "So, for instance, classically, nature decides that at some temperature the mismatched moments agree that they will all point to 120 degrees relative to each other. So they're not all 100 percent happy but it's some compromise that establishes an ordered state."

From there, he added, "The idea is to take a frustrated lattice where you have already suppressed the ordered state, and add quantum fluctuations to it, which take over as you cool the material. Magnetic frustration lowers the ordering temperature enough so that quantum fluctuations eventually take over and the system can stabilize into a fundamentally disordered quantum spin state."

Wilson continued: "That's the paradigm of what people are looking for; however, some materials may seem to display this state when actually, they don't. For instance, all real materials have disorder, such as chemical or structural disorder, and this can also prevent the magnetic moments from talking to each other effectively and becoming ordered. In such a case, Wilson says, "They might form a disordered state, but it's more of a frozen, or static, disordered state than it is a dynamic quantum state.

"So, if I have a magnetic system that doesn't order at the lowest temperatures I can measure, it can be tricky trying to understand whether what I'm measuring is an intrinsic quantum spin liquid fluctuating type of state or a frozen, extrinsic, chemically driven disordered state. That is always debated."

Among the most interesting findings about this new material, Wilson said, is that even at the lowest measurable temperature - .005 degree Centigrade above absolute zero - it still doesn't order.

"However, in this material we can also apply a magnetic field, which breaks this competition engendered by magnetic frustration, and then we can drive it to order, inducing a special kind of antiferromagnetic state," he added.

"The reason that's important is because this special state is very delicate and a very good fingerprint for how much chemical disorder there is in the system and its influence on the magnetic ground state. The fact that we can drive this field-driven state tells us that the disordered state we see at low temperature with zero magnetic field is indeed an intrinsically quantum disordered state, consistent with being a quantum spin liquid state."

Research paper

Related Links
University of California - Santa Barbara
Space Technology News - Applications and Research

Thanks for being there;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Monthly Supporter
$5+ Billed Monthly

paypal only
SpaceDaily Contributor
$5 Billed Once

credit card or paypal

Defrosting surfaces in seconds
Washington DC (SPX) Sep 02, 2019
In the future, a delayed flight due to ice will be no cause for a meltdown. A group of researchers at the University of Illinois at Urbana-Champaign and Kyushu University has developed a way to remove ice and frost from surfaces extremely efficiently, using less than 1% of the energy and less than 0.01% of the time needed for traditional defrosting methods. The group describes the method in Applied Physics Letters, from AIP Publishing. Instead of conventional defrosting, which melts all the ... read more

Comment using your Disqus, Facebook, Google or Twitter login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

China's satellite tests pulsar navigation for future deep space exploration

India not poor, has resources for space program says ISRO chief

Spacecraft carrying Russian humanoid robot docks at ISS

Vegetable cultivation in the Antarctic for the Moon and Mars

China's first medium-scale launcher with LOX LCH4 propellants ZQ-2 soliciting payloads worldwide

New Delhi in Talks With Moscow Over Rocket Engines for Indian Space Program

'Game-Changer' for Cosmic Research: NASA Chief Touts Nuclear Powered Spacecraft

Scientific Samples Make the Journey Back to Earth aboard SpaceX's Dragon

NASA engineers attach Mars Helicopter to Mars 2020 rover

NASA Invites Students to Name Next Mars Rover

NASA's Mars Helicopter Attached to Mars 2020 Rover

ExoMars rover ready for environment testing

China's newly launched communication satellite suffers abnormality

China launches first private rocket capable of carrying satellites

Chinese scientists say goodbye to Tiangong-2

China's space lab Tiangong 2 destroyed in controlled fall to earth

ESA and GomSpace Luxembourg sign contract for continued constellation management development

New Iridium Certus transceiver for faster satellite data now in live testing

KLEOS Space funding will start procurement of 2nd cluster of satellites

ThinKom Solutions Unveils New Multi-Beam Reconfigurable Phased-Array Gateway Solution for Next-Generation Satellites

In praise of the big pixel: Gaming is having a retro moment

FEFU scientists developed brand-new rapid strength eco-concrete

Smarter experiments for faster materials discovery

Defrosting surfaces in seconds

Exoplanets Can't Hide Their Secrets from Innovative New Instrument

Hints of a volcanically active exomoon

Canadian astronomers determine Earth's fingerprint

The dark side of extrasolar planets share surprisingly similar temperatures

ALMA shows what's inside Jupiter's storms

Young Jupiter was smacked head-on by massive newborn planet

Mission to Jupiter's icy moon confirmed

Giant Impact Disrupted Jupiter's Core

The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us.