An international team of scientists working to observe the effect of magnetic fields on light has successfully detected invisible forces within ordinary, non-magnetic metals, such as aluminum, copper, and gold—a feat they say was previously considered impossible.
The breakthrough detection could help to improve the understanding of how magnetic fields interact with metals used in everyday electronic devices, resulting in improvements for technologies ranging from smartphones to quantum computers.
“Trying to Hear a Whisper in a Noisy Room”
Although scientists can readily demonstrate how magnetic fields can bend an electric current, known as the Hall effect, showing how these currents affect light waves has not been as easy.
Efforts to demonstrate the effect on visual light wavelengths, involving what is called the optical Hall effect, have proven difficult due to the subtlety of the effect. This effect is even weaker in non-magnetic metals, leading scientists to suggest that detecting it in gold, copper, and aluminum may be impossible.
“It was like trying to hear a whisper in a noisy room for decades,” said Professor Amir Capua from the Institute of Electrical Engineering and Applied Physics at Hebrew University, who led the study along with Ph.D. candidate Nadav Am Shalom. “Everyone knew the whisper was there, but we didn’t have a microphone sensitive enough to hear it.”
According to Prof. Capula, even though scientists had long known that these invisible forces were present, figuring out how to detect the minuscule effects on light in the visible spectrum, where laser sources are abundant, remained a challenge. The professor said that detection is especially true for metals we think of as magnetically ‘quiet’, since they don’t stick to the refrigerator like magnets do. However, Capula also said that under the right conditions, these types of metals will respond to magnetic fields “just in extremely subtle ways.”
“Interestingly, even Edwin Hall, the greatest scientist of all, who discovered the Hall effect, attempted to measure his effect using a beam of light with no success,” the Professor recalled. “He summarizes in the closing sentence of his notable paper from 1881: ‘I think that, if the action of silver had been one tenth as strong as that of iron, the effect would have been detected. No such effect was observed.’ (E. Hall, 1881).”
Upgraded MOKE Makes Historic Optical Hall Effect Detection
To attempt to detect the invisible forces underlying the optical Hall effect for the first time, the researchers collaborated with Prof. Binghai Yan from the Weizmann Institute of Science, Prof. Igor Rozhansky from the University of Manchester, and Prof. Yan from Pennsylvania State University. According to the team’s published study, the first step required the researchers to upgrade a currently used method called the magneto-optical Kerr effect (MOKE). Designed with a visible spectrum laser, the MOKE measures how magnetism alters light’s reflection.
“Think of it like using a high-powered flashlight to catch the faintest glint off a surface in the dark,” they explain.
To enhance the MOKE device’s sensitivity in detecting invisible forces acting on non-metallic materials, the team combined a 440-nanometer blue laser with large-amplitude modulation of the external magnetic field. The team then used the device to test samples of copper, gold, aluminum, tantalum, and platinum. According to the team’s announcement, the improved MOKE detected magnetic “echoes” in all of the samples, “a feat previously considered near-impossible.”
“By tuning in to the right frequency—and knowing where to look—we’ve found a way to measure what was once thought invisible,” Capula said.
After further analysis of their tests, the team discovered that what had initially appeared as random ‘noise’ in the signal actually had a familiar quantum pattern linking how electrons move to their spin, known as spin-orbit coupling. Shalom said discovering the known pattern was like “discovering that static on a radio isn’t just interference—it’s someone whispering valuable information.”
“We’re now using light to ‘listen’ to these hidden messages from electrons,” Shalom said.
Potential Applications Include Quantum Computers and Spintronic Devices
Although the Hall effect is used in semiconductor manufacturing, current methods of detection typically involve physical wire connections and a process that the team described as “time-consuming and tricky,” especially when testing nanometer-sized components. Because their process merely requires the tester to shine a laser on the device to detect the effects of invisible forces, the team believes their breakthrough process offers a “non-invasive, highly sensitive tool for exploring magnetism in metals without the need for massive magnets or cryogenic conditions.”
The new process could help engineers build faster computer processors, more energy-efficient electronic systems, and extremely sensitive sensors with unprecedented accuracy, capable of detecting these invisible forces with unprecedented means and accuracy. The discovery could also have implications for magnetic memory designs, spintronic devices, and potentially quantum-based systems, such as quantum processors.
“This research turns a nearly 150-year-old scientific problem into a new opportunity,” said Prof. Capua.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.