Magnon circular birefringence: Polarization rotation of spin waves and its applications

July 31, 2017

An international team of researchers from Thailand, USA and Japan, has conducted a thorough study of an exotic behavior of material called "noncentrosymmetric antiferromagnet."The team, monitoring the behavior of the propagation of spin waves in magnetic material, has reported its findings [1], which show, for the first time, direct evidence of the nonreciprocal magnons.

A "circular birefringence" effect, where photons travelling inside a certain kind of crystal have different speeds depending on their circular polarization is fairly common. In other words, left-handed photons might travel faster than right-handed photons. Such an effect specifically appearing under a finite external magnetic field is the Faraday effect, where light polarization rotates as it propagates along the crystal with the rotation angle linearly depending on the field. There have been tremendous applications of this effect in modern optical and photonic technology. Optical isolator is one of such devices using the Faraday effect, whereas magneto-optical recording is based on its reflection variant, the Kerr effect.

Other systems also exhibit behaviors that resemble the circular birefringence effect. In an ordered magnetic material, a spin excitation can also propagate along the crystal. This excitation is called a "magnon." Similar to the polarization states of photons, magnons in an antiferromagnet also have two distinct states: left-circular and right-circular state. In most magnetic material, these two states have the same energy and are therefore indistinguishable. However, in a certain type of magnetic material, these two states of magnons behave differently due to a lack of spatial inversion symmetry in the crystal structure.

This phenomenon, called nonreciprocal magnons, has been predicted by Hayami et al. [2] However, there has been no direct observation of these nonreciprocal magnons until this work.

The research team performed neutron scattering experiments on single-crystal α-Cu2V2O7 and showed clear evidences of different energy-momentum dispersion relations between the left-circular and right-circular magnon propagation. The experimental data is confirmed by linear spin-wave calculations.

This work opens up a new regime of magnetic material which might find applications in magnon-based electronics (magnonics) such as the spin-wave field-effect transistor [3].
[1] G. Gitgeatpong, Y. Zhao, P. Piyawongwatthana, Y. Qiu, L. W. Harriger, N. P. Butch, T. J. Sato, and K. Matan, Phy. Rev. Lett. 119, 047201 (2017).

[2] S. Hayami, H. Kusunose, and Y. Motome, J. Phys. Soc. Jpn. 85, 053705 (2016).

[3] R. Cheng, M. W. Daniels, J.-G. Zhu, and D. Xiao, Sci. Rep. 6, 24223 (2016).

Tohoku University

Related Behavior Articles from Brightsurf:

Variety in the migratory behavior of blackcaps
The birds have variable migration strategies.

Fishing for a theory of emergent behavior
Researchers at the University of Tsukuba quantified the collective action of small schools of fish using information theory.

How synaptic changes translate to behavior changes
Learning changes behavior by altering many connections between brain cells in a variety of ways all at the same time, according to a study of sea slugs recently published in JNeurosci.

I won't have what he's having: The brain and socially motivated behavior
Monkeys devalue rewards when they anticipate that another monkey will get them instead.

Unlocking animal behavior through motion
Using physics to study different types of animal motion, such as burrowing worms or flying flocks, can reveal how animals behave in different settings.

AI to help monitor behavior
Algorithms based on artificial intelligence do better at supporting educational and clinical decision-making, according to a new study.

Increasing opportunities for sustainable behavior
To mitigate climate change and safeguard ecosystems, we need to make drastic changes in our consumption and transport behaviors.

Predicting a protein's behavior from its appearance
Researchers at EPFL have developed a new way to predict a protein's interactions with other proteins and biomolecules, and its biochemical activity, merely by observing its surface.

Spirituality affects the behavior of mortgagers
According to Olga Miroshnichenko, a Sc.D in Economics, and a Professor at the Department of Economics and Finance, Tyumen State University, morals affect the thinking of mortgage payers and help them avoid past due payments.

Asking if behavior can be changed on climate crisis
One of the more complex problems facing social psychologists today is whether any intervention can move people to change their behavior about climate change and protecting the environment for the sake of future generations.

Read More: Behavior News and Behavior Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to