When we encounter metals in our daily lives, we view them as shiny. That’s because common metal materials are reflective of the wavelengths of visible light and will reflect any light that strikes them. While metals are well suited to conduct electricity and heat, they are not usually thought of as a way to conduct light.
But in the booming field quantum materialsIncreasingly, researchers are finding examples that challenge expectations about how things should behave. In a new research published in science progressA team led by Dmitriy Basov, a professor of physics at Columbia University, Dmitriy Basov, describes a metal capable of conducting light. “These findings challenge our everyday experiences and common perceptions,” Basov said.
The work was led by Yiming Shao, who is now a postdoctoral researcher at Columbia University and has a Ph.D. A student when Basov moved his lab from the University of California, San Diego to New York in 2016. While working with Basov’s group, Shaw was exploring the optical properties of a semi-metallic substance known as ZrSiSe. in 2020 in Nature PhysicsShao and colleagues showed that ZrSiSe shares electronic similarities with graphene, the first so-called Dirac material discovered in 2004. However, ZrSiSe enhanced the rare electronic bonds for Dirac-like materials.
Whereas graphene is a single atom-thin carbon layer, ZrSiSe is a three-dimensional, layered metal crystal that behaves differently in the in-plane and out-of-plane directions, a property known as anisotropy. “It’s kind of like a sandwich: one layer acts as metal while the next layer acts as insulator,” Shaw explained. “When that happens, the light begins to interact unusually with the metal at certain frequencies. Instead of just bouncing, it can travel inside the material in a zigzag pattern, which we call hyperbolic diffusion.”
In their current work, Shaw and his collaborators at Columbia University and the University of California at San Diego observe zigzag motion of light, called hyperbolic waveguide patterns, through ZrSiSe samples of varying thicknesses. Such waveguides can guide light through a material, and here it results from mixing photons of light with electronic oscillations to form hybrid quasiparticles called plasmons.
Although the conditions were met to generate plasmons that can deterministically propagate in many layered metals, it was the unique range of electron energy levels, called the electron-band structure, of ZrSiSe that allowed the team to observe them in this material. Theoretical support to help explain these experimental results came from Andrey Rikhter in the Michael Fogler group at the University of California, San Diego, Umberto De Giovannini and Angel Rubio at the Max Planck Institute for the Structure and Dynamics of Matter, and Raquel Queiroz and Andrew Mellis at Columbia. (Rubio and Millis also belong to the Simmons Foundation’s Flatiron Institute)
Plasmons can “amplify” features in the sample, allowing researchers to see beyond the diffraction limit of optical microscopes, which otherwise cannot resolve details smaller than the wavelength of the light they are using. “By using hyperbolic plasmons, we can resolve features below 100 nanometers using infrared light that is hundreds of times longer,” Shao said.
ZrSiSe can be exfoliated to various thicknesses, Shao said, making it an interesting option for nano-optics research that favors ultrathin materials. But, it’s likely not the only material of value – from here, the group wants to explore others that share similarities with ZrSiSe but may have more suitable waveguiding properties. This could help researchers develop more efficient optical chips, and better nano-optics methods to explore fundamental questions about quantum materials.
“We want to use optical waveguide modes, as we found in this material and hope to find them in others, as messengers of interesting new physics,” said Basov.
Yinming Shao et al. Infrared plasmons propagate through a segmental nodal metal. science progress (2022). DOI: 10.1126 / sciadv.add6169
Columbia University Quantitative Initiative
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