A two-dimensional metasurface of germanium nanostructures is at the heart of a new technique Cornell researchers are using to generate static magnetic fields. The team reports converting light wave energy into lasting magnetization without relying on external magnets or magnetic materials, a development with potential for advances in spintronics and computing. Researchers created a sudden change in refractive index to halt a light wave’s magnetic field and transform it into a stationary pattern.

“We used an approach known as localized free carrier generation, which has advantages over other methods of nanoscale magnetization,” said Ph. D. candidate Shivaksh Rawat.

Metasurface Engineering Traps Light for Nanoscale Magnetization

The engineered germanium metasurface at the heart of this work enabled the conversion of light energy into a static magnetic field lasting approximately 300 femtoseconds, a duration equivalent to 20 cycles of the initiating mid-infrared light wave. This achievement bypasses the need for traditional magnets or magnetic materials to generate magnetism at the nanoscale, offering a fundamentally different approach to manipulating magnetic fields.

Researchers created this effect by illuminating the metasurface with a burst of near-infrared photons while mid-infrared light remained trapped within its nanostructures, releasing electrons and creating electron-hole pairs. The team’s modeling predicted this behavior, revealing that the near-infrared light generates a time-dependent change in the refractive index, which was key to the trapped mid-infrared light.

During this process, energy shifts to new, red-shifted light waves while the remaining energy becomes the kinetic energy of circulating free electrons, sustaining current loops that support the persistent magnetic field. Although losses limit the field’s duration, the observed 300 femtoseconds represents a significant timeframe for nanoscale magnetic control, opening possibilities for advanced technologies. “By rapidly changing the optical properties of an engineered metasurface, we were able to convert part of a passing light wave into a localized magnetic field that remained after the light had passed,” said Shivaksh Rawat.

This approach distinguishes itself through its material versatility; any non-metallic surface can theoretically function within the system. “One of the important contributions of our work is that our approach is material agnostic. Any non-metallic surface will work,” Rawat explained, highlighting the potential for broad applicability.

The researchers emphasize that their findings illuminate the energy redistribution processes within rapidly changing optical materials. The work, performed with support from the Cornell University Laboratory of Plasma Studies and the Cornell Center for Advanced Computing, could advance spintronics, data storage, and quantum computing by providing a novel pathway for manipulating magnetism without conventional materials.

We used an approach known as localized free carrier generation, which has advantages over other methods of nanoscale magnetization.
Shivaksh Rawat, Ph

Source: https://news.cornell.edu/stories/2026/09/researchers-use-light-generate-nanoscale-magnetization

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