Scientists have discovered that ultra-thin materials—just a few atoms thick—can naturally create tiny “cavities” that trap light and electrons.
This surprising finding helps explain why mysterious quantum effects, such as superconductivity and unusual magnetism, appear in these materials and how they could be controlled in the future.
The research, published in Nature Physics, was led by James McIver and his team at Columbia University and the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg.
Two-dimensional (2D) materials, like graphene, have fascinated scientists for years because they can behave in strange and powerful ways. In the right conditions, they can conduct electricity without resistance or show new kinds of magnetic behavior.
But no one fully understood why these effects appeared or how to tune them.
McIver’s team found that small stacks of these materials can naturally form cavities—tiny spaces that trap light and electrons in confined regions, changing how they move and interact.
The researchers made their discovery using a new terahertz (THz) spectroscopic technique. Terahertz light is a form of electromagnetic radiation between microwaves and infrared light, and it’s useful for probing quantum materials.
The team built a miniature spectroscope on a chip that could shrink THz light from one millimeter down to just a few micrometers—about 300 times smaller than a human hair.
This allowed them to watch how electrons behave inside 2D materials with unprecedented detail.
When they tested their device with graphene, they noticed something unexpected—standing waves forming inside the material.
These waves, created by the interaction of light and electrons, resembled the vibration of a guitar string.
In a guitar, the string’s fixed ends create standing waves that define musical notes. Similarly, in this experiment, the edges of the 2D material acted like mirrors that reflected light and electrons back and forth, creating confined waves called plasmon polaritons.
Usually, scientists need mirrors to trap light and create a cavity. But here, the researchers found that the material’s own edges did the job.
Each layer in their multi-layered device acted like a separate cavity just tens of nanometers apart, and the waves in these layers interacted with each other—much like connecting two guitar strings changes the note they produce.
This strong coupling between light and electrons could explain why certain 2D materials show exotic quantum behaviors.
To understand these effects, the researchers developed a simple analytical model that could predict the results using only a few geometric details of the material.
With this tool, they can now design new materials and experiments to control how light and matter interact. Adjusting conditions such as temperature, magnetic field, or electron density could reveal what drives different quantum phases.
The new chip-based THz spectroscope can also be used to study many other 2D materials and types of quasiparticles—tiny hybrid entities that behave like waves and particles at the same time. McIver’s team is already exploring new samples in both Hamburg and New York.
“We didn’t expect to see these cavity effects,” said postdoctoral researcher Hope Bretscher. “But now that we can, it opens an exciting way to manipulate quantum materials and understand their hidden behaviors.”
