Kagome Metal Demonstrates Exceptional Potential for Advanced Optical Technologies

In a recent study published in the journal Nature Communications, researchers from Florida State University discussed the generation of plasmon polaritons. These are nanoscale-level linked waves of electrons and electromagnetic fields in a material usually brought on by light or other electromagnetic waves.

In traditional Japanese basket weaving, the ancient “Kagome” design in many handcrafted creations is characterized by a symmetrical pattern of interlaced triangles with shared corners. Scientists have used the Kagome moniker in quantum physics to refer to a family of materials whose atomic structures closely resemble this characteristic lattice arrangement.

In 2019, researchers have been attempting to get more insight into the properties and possible uses of the newest family of Kagome metals.

The behavior of electrons in Kagome metals is more complex than in normal metals, and plasmons have not been studied as much in previous studies. To better understand the characteristics that make the metal cesium vanadium antimonide, also known by its chemical formula, CsV3Sb5, an attractive candidate for more accurate and effective photonic technologies, the researchers at FSU investigated it in this study.

For the first time, the researchers discovered that CsV3Sb5 contains plasmons and that the thickness of the metal affects the plasmons' wavelength.

Additionally, they discovered that altering the laser's frequency while it was directed at the metal changed the behavior of the plasmons, causing them to change into “hyperbolic bulk plasmons,” which dispersed throughout the material as opposed to remaining limited to its surface. These waves could travel more efficiently because they were losing less energy than they had previously.

Hyperbolic plasmon polaritons are rare in natural metals, but our research reveals how electron interactions can create these unique waves at the nanoscale. This breakthrough is key for advancing technologies in nano-optics and nano-photonics.

Guangxin Ni, Assistant Professor, Department of Physics, Florida State University

The researchers grew single crystals of CsV3Sb5 and then applied thin flakes of the material onto specifically prepared gold surfaces to investigate the interaction between plasmons and the metal.

Employing lasers to perform scanning infrared nano-imaging, they noticed intriguing changes in the metal's plasmon polaritons, which are waves of electrons interacting with electromagnetic fields.

What makes CsV3Sb5 interesting is how it interacts with light on a very small scale, what is known as nano-optics. We found that over a wide range of infrared light frequency, the correlated electrical properties within the metal triggered the formation of hyperbolic bulk plasmons.

Hossein Shiravi, Study Lead Author and Graduate Research Assistant, Florida State University

Thanks to the hyperbolic pattern, less energy is lost. The team's discoveries shed new light on the behavior of Kagome metal CsV3Sb5 under different circumstances, giving researchers a more precise understanding of its characteristics and possible practical uses.

Hyperbolic plasmon polaritons can offer a range of amazing nano-optical features and abilities. They have the potential to boost optical communication systems, allow for super-clear imaging beyond current limits, and make photonic devices work better. They could also be useful for sensing things like environmental changes and medical diagnostics because they react strongly to their surroundings. These qualities make them key for advancing future optical and photonic technologies.

Guangxin Ni, Assistant Professor, Department of Physics, Florida State University

The peculiar electrical and optical features of the CsV3Sb5 metal, including the capacity to steer plasmon waves in a particular direction, made it an interesting candidate for plasmon study. Recent developments in nanoscale imaging technology enabled the researchers to finish their job.

Ni said, “Electronic losses typically encountered in conventional metals have previously complicated efforts to observe exotic light-matter coupling effects, including hyperbolic polaritons. This is part of what makes this an exciting breakthrough. It will be interesting to continue exploring nano-optical phenomena in unconventional metals owing to their potential to contribute to future technologies.”

Aakash Gupta, a graduate student from FSU, is the co-author of the study. The research had collaborators from the University of California Santa Barbara, Oak Ridge National Laboratory in Tennessee, Tsinghua University in China, and Germany’s University of Stuttgart, Leipzig University, and Institute of Ion Beam Physics and Materials Research.

The study received funding from the US Department of Energy and National Science Foundation.

Journal Reference:

Shiravi, H., et al. (2024) Plasmons in the Kagome metal CsV3Sb5. Nature Communications. doi.org/10.1038/s41467-024-49723-x.