Terahertz detection on a chip closer to reality

Terahertz detection on a chip closer to reality

Technology News |
Physicists at the University of California, Riverside say they have discovered an electrical detection method for terahertz (THz) electromagnetic waves, which are otherwise extremely difficult to detect.
By Rich Pell

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The finding is based on a magnetic resonance phenomenon in anti-ferromagnetic materials – or antiferromagnets – which offer unique advantages for ultrafast and spin-based nanoscale device applications. The discovery, say the scientists, could help miniaturize the detection equipment on microchips and enhance sensitivity.

In their work, the researchers generated a spin current – an important physical quantity in spintronics representing a “flow of spins” – in an antiferromagnet and were able to detect it electrically. To accomplish this, they used terahertz radiation to pump up magnetic resonance in chromia (chromium oxide) to facilitate its detection.

In ferromagnets, such as a bar magnet, electron spins point in the same direction – up or down – thus providing collective strength to the materials. Conversely, in antiferromagnets the electron spins cancel each other out, with half of the spins pointing in the opposite direction of the other half, either up or down.

The electron has a built-in spin angular momentum, which can precess – i.e., change the orientation of the rotational axis of a rotating body – the way a spinning top precesses around a vertical axis. When the precession frequency of electrons matches the frequency of electromagnetic waves generated by an external source acting on the electrons, magnetic resonance occurs – manifested in the form of a greatly enhanced signal that is easier to detect.

In order to generate such magnetic resonance, the researchers worked with 0.24 THz of radiation produced at the Institute for Terahertz Science and Technology’s Terahertz Facilities at the Santa Barbara campus. This, say the researchers, 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,” says Jing Shi, a professor in the Department of Physics and Astronomy.

This has implications in the field of communications, says Shi, which currently uses gigahertz microwaves.

“For higher bandwidth, however, the trend is to move toward terahertz microwaves,” Shi says. “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 technology has been disclosed to UCR Technology Commercialization and is patent pending. For more, see “Spin current from sub-terahertz-generated antiferromagnetic magnons.”

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