A new approach has allowed researchers at Aalto University to design a kind of meta­material that has so far been beyond the reach of existing technologies. 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 new meta­material takes 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. The NME 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. Most of the proposed approaches would only work for micro­waves and not visible light, and they also couldn’t be fabricated with available technology,” says Shadi Safaei Jazi. His team 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. When the brightness is different between the two sides, 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,” says Safaei. 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. (Source: Aalto U.)

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

Link: Designer Materials and Devices, Dept. of Electronics and Nanoengineering, Aalto University, Aalto, Finland