Metamaterial can trap light to become 10 times more magnetic

Such a phenomenon can help in the development of magnetic lasers and magneto-optical memory devices.
Jijo Malayil
Representational image of trapped light.jpg
Representational image of trapped light.


A study by a team of researchers showed that trapping light in magnetic materials enhances its intrinsic properties. The work gains relevance as the development of magnetic lasers, magneto-optical memories, and upcoming quantum transduction applications all depend on magnets having optical solid responses. 

The study, which was led by Vinod M. Menon and his research group at The City College of New York (CCNY), is published in the journal Nature.

The team's work features a metamaterial that is made of chromium, sulfur, and bromine, which belongs to a class known as magnetic van der Waals materials. The magnetic superconductor contains firmly bound excitons called quasiparticles with robust optical interactions. Because of this, the substance has the ability to capture light on its own. The research demonstrates that this material's optical sensitivities to magnetic events are orders of magnitude greater than those of conventional magnets.

"Since the light bounces back and forth inside the magnet, interactions are genuinely enhanced. To give an example, when we apply an external magnetic field the near-infrared reflection of light is altered so much, the material basically changes its color. That's a pretty strong magneto-optic response," said Dr. Florian Dirnberger, the lead author of the study, in a statement

Rare phenomenon

Controlling electromagnetic phenomena is at the core of modern technology. You have control over magnets, light, electricity, charged particles, or any combination of these. Since there aren't many situations where light and magnetism interact so strongly, many magneto-optical systems call for sensitive light detection.

"Ordinarily, light does not respond so strongly to magnetism. This is why technological applications based on magneto-optic effects often require the implementation of sensitive optical detection schemes," said Menon, senior author and a professor at CCNY.

In contrast, the team noticed that when the light enters the material, it exhibits interaction with the excitons in a way that it is trapped inside. This results in it becoming 10 times more magnetic.

"Technological applications of magnetic materials today are mostly related to magneto-electric phenomena. Given such strong interactions between magnetism and light, we can now hope to one day create magnetic lasers and may reconsider old concepts of optically controlled magnetic memory." Rezlind Bushati, a graduate student in the Menon group, who also contributed to the experimental work.

The US Air Force Office of Scientific Research, the Division of Materials Research of the National Science Foundation (NSF), the NSF CREST IDEALS Center, DARPA, and the German Research Foundation all provided funding for the CCNY research.

Study abstract

Controlling quantum materials with light is of fundamental and technological importance. By utilizing the strong coupling of light and matter in optical cavities recent studies were able to modify some of their most defining features. Here we study the magneto-optical properties of a van der Waals magnet that supports strong coupling of photons and excitons even in the absence of external cavity mirrors. In this material—the layered magnetic semiconductor CrSBr—emergent light–matter hybrids called polaritons are shown to substantially increase the spectral bandwidth of correlations between the magnetic, electronic, and optical properties, enabling largely tunable optical responses to applied magnetic fields and magnons. Our results highlight the importance of exciton–photon self-hybridization in van der Waals magnets and motivate novel directions for the manipulation of quantum material properties by strong light–matter coupling.

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