Physicists discover new method to detect terahertz waves

The team used magnetic resonance in anti-ferromagnetic materials to make the waves easier to see. Jing Shi, a professor in the Department of Physics and Astronomy at UC Riverside, led the team who made the discovery. (Image credit: UC Riverside)

Terahertz electromagnetic waves, a unit of electromagnetic wave frequency, are typically extremely difficult to detect. But a team of physicists has discovered a new way to detect for terahertz based on a magnetic resonance phenomenon in anti-ferromagnetic materials. These materials, known as antiferromagnets, have many advantages for ultrafast and spin-based nanoscale device applications.

So how did they do it? The team, led by physicist Jing Shi from the University of California, Riverside, generated what’s known as a spin current, an important physical quantity in spintronics - the study of the intrinsic spin of the electron and its magnetic movement - in an antiferromagnet, which allowed them to detect it electrically. To make the current easier to see, they used terahertz radiation to increase the magnetic resonance in chromia.

Because the electron has a built-in spin angular momentum, it can change the orientation of the axis in the way a spinning top moves about a vertical axis. When the precession frequency of electrons and the electromagnetic waves create by an external source match up, it results in magnetic resonance manifesting in an enhanced form that’s easier to detect.

The team generated the magnetic resonance using 0.24 terahertz of radiation produced at the Institute for Terahertz Science and Technology's Terahertz Facilities at the Santa Barbara campus. The result closely matched the precession frequency of electrons in chromia. The magnetic resonance that followed resulted in the generation of a spin current that the researchers converted into a DC voltage.

"We were able to demonstrate that antiferromagnetic resonance can produce an electrical voltage, a spintronic effect that has never been experimentally done before," said Shi, a professor in the Department of Physics and Astronomy.

The ability to detect terahertz electromagnetic waves opens up possibilities for various applications, such as miniaturizing detection equipment on microchips and enhance sensitivity. It’s also a big step forward in using terahertz microwaves for technology communication and higher bandwidth. Currently, communication technology relies on gigahertz microwaves. Using terahertz instead would allow for faster information transmission.

"For higher bandwidth, however, the trend is to move toward terahertz microwaves," Shi said. "The generation of terahertz microwaves is not difficult, but their detection is. Our work has now provided a new pathway for terahertz detection on a chip."

The team’s findings were published in the latest issue of Nature.

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