Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Spin liquids − back to the roots

22.06.2017

Researchers from Augsburg, Oxford, and Nanjing report in Nature Communications on a neutron experiment exposing experimental signatures of a low-temperature state predicted 44 years ago

Since 1973, Anderson's resonating valence bond model remains a paradigm for microscopic description of quantum spin liquids in frustrated magnets. It is of fundamental interest as a building unit for more complex quantum-mechanically entangled states that can be used in quantum computing.


Sketch of Anderson's resonating valence bond state formed by localized spins shown in green. The pair of opposite spins ("valence bond") is highlighted by a yellow oval.

© Universität Augsburg, EP VI/EKM

Researchers from the Chair of Experimental Physics VI/EKM report in Nature Communications first experimental signatures of excitations from this fundamental state exposed by a neutron-scattering study performed in collaboration with Rutherford Appleton Laboratory in Oxford and Renmin University of China.

Liquids entail haphazardly moving particles that can be correlated on the short-range scale, but lack any long-range order. In contrast to gases, liquids are only weakly compressible, because separations between their particles are small, and inter-particle interactions strong. A liquid-like state can also form in magnets, where electron spins act as individual particles.

Neighboring spins in a spin liquid strongly interact with each other, but evade long-range order, unlike, for example, in ferromagnets, where parallel alignment of spins throughout the crystal generates macroscopic magnetization that can drive rotation of the motor of an electric car or interact with Earth's magnetic field in a compass.

Spins are pairwise correlated, but remain disordered

Back in 1973 American physicist and eventual Nobel prize winner Philip W. Anderson contemplated a model, where spins are arranged on a triangular plane, and only adjacent spins (nearest neighbors) interact. These interactions trigger spins to be mutually antiparallel, but a global antiparallel (antiferromagnetic) configuration is prevented by the triangular arrangement.

The quantum-mechanical description proposed by Anderson is based on the idea of pair-wise correlations, where different pairs form, as shown in the Figure. In each pair, spins are opposite to each other forming resonating valence bonds (RVBs), the name used to emphasize close resemblance with chemical bonds between atoms in molecules and crystals.

The RVB state is quantum-mechanically entangled, it can not be represented by a simple combination of individual spins. Such entanglement opens new possibilities for high-performance calculations in a quantum computer. Despite far-reaching implications for present-day theories, the validity of Anderson's model of the RVB state was in the meantime questioned, and signatures of the RVB state were nowhere to be seen experimentally.

New substance with the triangular spin geometry

"The formation of Anderson's RVB state requires magnetic frustration, the presence of competing interactions between the spins" explains Dr. Alexander Tsirlin, the leader of the young research group at the Center for Electronic Correlations and Magnetism at the Institute of Physics in Augsburg.

This is made possible by a new substance, YbMgGaO4, that was prepared and investigated in collaboration with Renmin University of China and Rutherford Appleton Lab in Oxford, UK. The original chemical compound features regular triangular arrangement of magnetic moments, which are localized on the ytterbium atoms (see the Figure).

Earlier work by the team confirmed that even at temperatures of several hundredths of degree above the absolute zero spins remain dynamic in the form of a spin liquid evading long-range order, a pre-condition for building the long-sought RVB state.

Magnetic excitations follow predictions of Anderson's theory

Neutrons scatter from crystals changing direction and energy, and providing researchers with a sensitive probe of correlations between the spins. Neutron-scattering experiments on YbMgGaO4 reveal two distinct regimes. At higher transfer energies, where neutrons trigger high-energy excitations, experimental observations are in perfect agreement with Anderson's RVB model.

"After several decades, signatures of the nearest-neighbor RVB state have been finally observed", explains Prof. Dr. Philipp Gegenwart, head of the Chair of Experimental Physics VI / EKM. Less clear remains the experimental response at low energies, where Anderson's RVB picture fails. This part of the spectrum appears to be intertwined with magnetic interactions beyond Anderson's model, and may give researchers further clues as to why the RVB state has formed.


Publication

Yuesheng Li, Devashibhai Adroja, David Voneshen, Robert I. Bewley, Qingming Zhang, Alexander A. Tsirlin, and Philipp Gegenwart, Nearest-neighbor resonating valence bonds in YbMgGaO4, Nat. Commun. 8 (2017), 15814.

http://www.nature.com/articles/ncomms15814


Contact persons:

Prof. Dr. Philipp Gegenwart and Dr. Alexander Tsirlin
Chair of Experimental Physics VI / EKM
Institute of Physics / Center of Electronic Correlations and Magnetism
University of Augsburg
86135 Augsburg
Phone: +49(0)821/598‐3651
philipp.gegewart@physik.uni‐augsburg.de, alexander.tsirlin@physik.uni-augsburg.de

Weitere Informationen:

http://www.nature.com/articles/ncomms15814

Klaus P. Prem | idw - Informationsdienst Wissenschaft
Further information:
http://www.uni-augsburg.de/

Further reports about: Electronic Experimental Physics Spin bonds crystals liquids magnetism

More articles from Physics and Astronomy:

nachricht Meteoritic stardust unlocks timing of supernova dust formation
19.01.2018 | Carnegie Institution for Science

nachricht Artificial agent designs quantum experiments
19.01.2018 | Universität Innsbruck

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

Im Focus: Room-temperature multiferroic thin films and their properties

Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.

Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Let the good tubes roll

19.01.2018 | Materials Sciences

How cancer metastasis happens: Researchers reveal a key mechanism

19.01.2018 | Health and Medicine

Meteoritic stardust unlocks timing of supernova dust formation

19.01.2018 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>