Cornell researchers have demonstrated a way to generate strong, localized magnetic fields with light instead of conventional magnets, a laboratory advance they say could inform future work in computing and data storage.
The team used an engineered surface that traps mid-infrared light and then struck it with a short burst of higher-energy light. The interaction converted part of the trapped optical wave into a stationary magnetic pattern, according to a study published in Advanced Science.
The method relies on a sudden change in a material's optical properties known as a time interface. When light crosses a physical boundary, such as air and water, some is reflected and some transmitted. A rapid change in refractive index can produce a similar effect in time and can also create a static, zero-frequency mode.
Researchers built a two-dimensional metasurface from a rectangular array of germanium nanostructures designed to trap infrared light. A near-infrared pulse freed electrons from germanium atoms and left electron holes, rapidly changing the surface's refractive index while the first light wave remained inside.
Some of the trapped energy shifted into redder light waves. The rest became the kinetic energy of circulating free electrons that formed current loops and sustained magnetic fields in localized hot spots.
The magnetization lasted about 300 femtoseconds under normal conditions, roughly three 10-trillionths of a second. Researchers said that brief period still represents about 20 cycles of the mid-infrared wave that created the field.
Doctoral student Shivaksh Rawat said the localized free-carrier approach is material agnostic and could work with nonmetallic surfaces. He said the experiment also helps explain how energy is redistributed when optical materials change rapidly.
Rawat led the work with postdoctoral researcher Samyobrata Mukherjee in the laboratory of engineering physics professor Gennady Shvets. The team said the method could open research paths in spintronics, magnetic data storage, photonic and quantum computing, and precise control of magnetic environments.
The University of Dayton Research Institute, Office of Naval Research and Army Research Office supported the work. Researchers also used computing resources at Cornell's Laboratory of Plasma Studies with help from the Cornell Center for Advanced Computing.
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