Metals are canonical plasmonic media at infrared and optical wavelengths, allowing one to guide and manipulate light at the nanoscale. Metals are excellent at transferring heat and electricity, but they aren’t frequently considered a means of conducting light.

A new study by Columbia University reports about a metal that can conduct light through it.

Scientists have been investigating the optical properties of a semimetal material known as ZrSiSe. In 2020, they found that ZrSiSe shares electronic similarities with graphene. Enhanced electronic correlations, uncommon for Dirac semimetals, are present in ZrSiSe.

Unlike graphene, a single, atom-thin carbon layer, ZrSiSe is a three-dimensional metallic crystal. It is made of layers that behave differently in the in-plane and out-of-plane directions. This property is known as anisotropy.

Yinming Shao, now a postdoc at Columbia, said, “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. Instead of bouncing off, it can travel inside the material in a zigzag pattern, which we call hyperbolic propagation.”

In this study, scientists used ZrSiSe samples of various thicknesses to witness such zigzag movements of light or so-called hyperbolic waveguide modes. These waveguides, which are plasmons, are produced when light photons combine with electron oscillations to form hybrid quasiparticles that may direct light through a material.

Scientists noted, “It is the unique range of electron energy levels, called electronic band structure, of ZrSiSe that allowed the team to observe them in this material.”

Plasmons can “magnify” features in a sample, enabling scientists to see past the diffraction limit of optical microscopes, which are otherwise unable to distinguish details smaller than the wavelength of light they utilize.

Shao said, “Using hyperbolic plasmons, we could resolve features less than 100 nanometers using infrared light that’s hundreds of times long.”

“ZrSiSe can be peeled to different thicknesses, making it an interesting option for nano-optics research that favors ultra-thin materials. But, it’s likely not the only material to be valuable—from here, the group wants to explore others that share similarities with ZrSiSe but might have even more favorable waveguiding properties. That could help us develop more efficient optical chips and better nano-optics approaches to explore fundamental questions about quantum materials.”

Journal Reference:

  1. Yinming Shao et al. Infrared plasmons propagate through a hyperbolic nodal metal. Science Advances (2022). DOI: 10.1126/sciadv.add6169