Overview

Physicists have found evidence of waveguiding in a unique type of metal, known as ZrSiSe. This metal allows light to travel through it, defying the common rules of physics.

The science and other stuff to know

Metals are great conductors of heat and electricity, but they don’t conduct light. Typically, they are reflective at visible light wavelengths, and any light that strikes them will bounce off.

However, new research by physicists at Columbia University is challenging expectations on how metals should behave. Published in Science Advances, the study investigates the optical properties of a semimetal material called ZrSiSe.

Dmitri Basov, Higgins Professor of Physics at Columbia University who led the research team, claims ZrSiSe not only has electronic properties but can also allow light to travel through it. “These results defy our daily experiences and common conceptions,” said Basov, in a statement.

“It’s sort of like a sandwich: One layer acts like a metal while the next layer acts like an insulator. When that happens, the light starts to interact unusually with the metal at certain frequencies,” first study author Yinming Shao explained. “Instead of just bouncing off, it can travel inside the material in a zigzag pattern, which we call hyperbolic propagation.”

According to the study, the team observed this zigzag light movement when they used ZrSiSe samples of different thicknesses. This movement is also called a hyperbolic waveguide, and it results from photons of light mixing with electron oscillations to create hybrid quasiparticles called plasmons.

While many kinds of layered metals can produce plasmons, it’s ZrSiSe’s distinct range of electron energy levels or electronic band structure that enables it to move light.

So what?

This research counters expectations on how metals conduct light and it may push imaging beyond optical diffraction limits.

According to Shao, ZrSiSe can be pealed to different thicknesses. Thus, it’s an intriguing option for nano-optics research that could help solve fundamental problems with quantum materials. In addition, ZrSiSe and similar materials could help researchers develop more efficient optical chips.

What’s next?

Researchers believe ZrSiSe isn’t the only semimetal that can allow light to travel through it. The team is planning to experiment with other quantum materials that share similarities with ZrSiSe but might have even more favorable waveguiding properties.

“We want to use optical waveguide modes, like we’ve found in this material and hope to find in others, as reporters of interesting new physics,” Basov said.