Cornell researchers create nanoscale
Researchers at Cornell University have generated static magnetic fields at the nanoscale by using a metasurface to trap light and create a 'time interface'.
Cornell University researchers have generated strong, static magnetic fields at the nanoscale using only illumination and an engineered surface. Their technique, published in the journal Advanced Science, converts part of a trapped light wave's energy into a persistent magnetization without any external magnets or magnetic materials.
Shivaksh Rawat, a Ph.D. candidate working with Professor Gennady Shvets, and postdoc Samyobrata Mukherjee described a new method based on a 'time interface.' When a light wave experiences a sudden change in the optical properties of its medium, a time interface, it can excite a static, zero-frequency mode. This stops part of the illumination's oscillating magnetic field and turns it into a stationary magnetic pattern.
Engineering a time interface with illumination
Researchers used a two-dimensional metasurface, a rectangular array of germanium nanostructures designed to trap mid-infrared illumination. They then illuminated this structure with an intense, short burst of higher-energy near-infrared photons while the mid-infrared illumination was still trapped inside.
Their modeling showed the near-infrared illumination released electrons from the germanium atoms, creating many free electrons and 'electron holes.' This rapid generation of charge carriers creates a time-dependent change in the refractive index, acting as a time interface for the trapped mid-infrared illumination. Rawat explained they used an approach known as localized free carrier generation, noting that one of the important contributions of their work is that their approach is material agnostic, meaning any nonmetallic surface will work.
A persistent magnetic hot spot
During the time interface, some energy from the trapped illumination shifts to new, red-shifted illumination waves. The rest becomes the kinetic energy of circulating free electrons. These electrons support current loops that sustain a persistent magnetic field in localized hot spots on the metasurface.
In an ideal, lossless system, this magnetization would last forever. Under normal experimental conditions, the generated magnetic field persisted for about 300 femtoseconds. While that is an extraordinarily short time, roughly three 10-trillionths of a second, it equals about 20 cycles of the mid-infrared illumination wave that created it.
Implications for future technologies
Rawat stated that their work demonstrates a fundamentally new method for creating strong magnetic fields using illumination rather than conventional magnets. The research helps explain how energy is redistributed in rapidly changing optical materials.
By showing how illumination can both transmit information and create localized magnetism, the work opens new research directions at the intersection of photonics and magnetism. The technique could have implications for several advanced fields.
The approach could advance spintronics, magnetic data storage, and photonic and quantum computing. It also offers a path for the precise control of magnetic environments at the nanoscale. The work, funded through Cornell, is part of broader efforts to develop time-varying photonics and all-optical control of material properties.
