Researchers One Step Closer to True One-Way Glass

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Scientists at Aalto University have proposed a three-dimensional metamaterial with an isotropic effect in the visible spectral range.

The new metamaterial is formed by randomly oriented bi-material nanocylinders in a host medium. Image credit: Ihar Faniayeu / Aalto University.

Unlike natural materials, metamaterials and metasurfaces can be tailored to have specific electromagnetic properties, which means scientists can create materials with features desirable for industrial applications.

The newly-proposed metamaterial takes an advantage of the nonreciprocal magnetoelectric (NME) effect.

“The NME effect implies a link between specific properties of the material (its magnetization and polarization) and the different field components of light or other electromagnetic waves,” said first author Shadi Safaei Jazi and colleagues.

This effect is negligible in natural materials, but scientists have been trying to enhance it using metamaterials and metasurfaces because of the technological potential this would unlock.

“So far, the NME effect has not led to realistic industrial applications,” Jazio said.

“Most of the proposed approaches would only work for microwaves and not visible light, and they also couldn’t be fabricated with available technology.”

“We designed an optical NME metamaterial that can be created with existing technology, using conventional materials and nanofabrication techniques.”

The new material opens up applications that would otherwise need a strong external magnetic field to work — for example, creating truly one-way glass.

“Glass that’s currently sold as ‘one-way’ is just semi-transparent, letting light through in both directions,” Jazi said.

“When the brightness is different between the two sides (for example, inside and outside a window), it acts like one-way glass.”

“But an NME-based one-way glass wouldn’t need a difference in brightness because light could only go through it in one direction.”

“Just imagine having a window with that glass in your house, office, or car.”

“Regardless of the brightness outside, people wouldn’t be able to see anything inside, while you would enjoy a perfect view from your window.”

“If technology succeeds, this one-way glass could also make solar cells more efficient by blocking the thermal emissions that existing cells radiate back toward the sun, which reduces the amount of energy they capture.”

The work was published in the journal Nature Communications.

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S. Safaei Jazi et al. 2024. Optical Tellegen metamaterial with spontaneous magnetization. Nat Commun 15, 1293; doi: 10.1038/s41467-024-45225-y

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