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Researchers image quasiparticles that could lead to faster circuits, higher bandwidths

Zhe Fei pointed to the bright and dark vertical lines running across his computer screen. This nano-image, he explained, shows the waves associated with a half-light, half-matter quasiparticle moving inside a semiconductor. “These are waves just like water waves,” said Fei, an Iowa State University assistant professor of physics and astronomy and an associate of the U.S. Department of Energy’s Ames Laboratory. “It’s like dropping a rock on the surface of water and seeing waves. But these waves are exciton-polaritons.” Exciton-polaritons are a combination of light and matter. Like all quasiparticles, they’re created within a solid and have physical properties such as energy and momentum. In this study, they were launched by shining a laser on the sharp tip of a nano-imaging system aimed at a thin flake of molybdenum diselenide (MoSe2), a layered semiconductor that supports excitons. Excitons can form when light is absorbed by a semiconductor. When excitons couple strongly with photons, they create exciton-polaritons. It’s the first time researchers have made real-space images of exciton-polaritons. Fei said past research projects have used spectroscopic studies to record exciton-polaritons as resonance peaks or dips in optical spectra. Until recent years, most studies have only observed the quasiparticles at extremely cold temperatures – down to about -450 degrees Fahrenheit. But Fei and his research group worked at room temperature with the scanning near-field optical microscope in his campus lab to take nano-optical images of the quasiparticles.”

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